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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

Integration of multiple flexible electrodes for realtime detection of barrier formation with spatial resolution in a gut-on-chip system

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Microsystems & Nanoengineering 2024年第1期10卷 105-114页

作者： Mara Lucchetti Gabriel Werr Sofia johansson Laurent Barbe Léa Grandmougin Paul Wilmes Maria Tenje Luxembourg Centre for Systems Biomedicine(LCSB) University of LuxembourgEsch-sur-Alzette L-4362Luxembourg Division of Biomedical Engineering Department of Materials Science and EngineeringScience for Life LaboratoryUppsala University75121 UppsalaSweden Department of Life Sciences and Medicine Faculty of ScienceTechnology and MedicineUniversity of LuxembourgEsch-sur-Alzette L-4362Luxembourg

In healthy individuals,the intestinal epithelium forms a tight barrier to prevent gut bacteria from reaching blood *** study the effect of probiotics,dietary compounds and drugs on gut barrier formation and disruption,human gut epithelial and bacterial cells can be cocultured in an in vitro model called the human microbial crosstalk(HuMiX)gut-on-a-chip ***,we present the design,fabrication and integration of thin-film electrodes into the HuMiX platform to measure transepithelial electrical resistance(TEER)as a direct readout on barrier tightness in *** various aspects of the HuMiX platform have already been set in their design,such as multiple compressible layers,uneven surfaces and nontransparent materials,a novel fabrication method was developed whereby thin-film metal electrodes were first deposited on flexible substrates and sequentially integrated with the HuMiX system via a transfer-tape ***,to measure localized TEER along the cell culture chamber,we integrated multiple electrodes that were connected to an impedance analyzer via a *** further developed a dynamic normalization method because the active measurement area depends on the measured TEER *** fabrication process and system setup can be applicable to other barrier-on-chip *** a proof-of-concept,we measured the barrier formation of a cancerous Caco-2 cell line in real-time,which was mapped at four spatially separated positions along the HuMiX culture area.

关键词： barrier system multiple

北欧岩高兰(Empetrum)生态系统:功能及其对环境变化的敏感性

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AMBIO－人类环境杂志 2000年第2期29卷 90-97页

作者： Knud Tybirk Marie-Charlotte Nilsson Anders Michelsen Hanne Lakkenborg Kristensen Anna shevtsova Morten Tune Strandberg marianne johansson Knud Erik Nielsen Torben Riis-Nielsen Beate Strandberg Ib Johansen 萨仁 NERI Dept.of Landscape Ecology Grenvej 14 DK-8410 Rnde Denraark Forest Vegetation Ecology SLU SE-90183 Ume Sweden Plant Ecology Φ.Farimagasgade 2DDK-1353 Copenhagen K Denmark of Forest Ecology Forest and Landscape Research Institute Hrsholm Kongevej 29 DK-2970 Hrshoim Denmark Biology University of Turku FIN-20014 Turku Finland Terrestrial Ecology NERI Vejlsvej 25 DK-8600 SilkeborgDenmark of Mycology Botanical Institute University of Copenhagen .Farimagasgade 2D DK-1353 Copenhagen K Denmark Forest Ecology Forest and Landscape Research Institute Hrsholm Kongevej 29 DK-2970 Hrsholm Denmark Plant Ecology University of Copenhagen .Farimagasgade 2D DK-1353 Copenhagen K Denmark

本文回顾了关于北欧地区岩高兰(Empetrum nigrum ***和***)生态系统的知识。因为岩高兰叶片及其枯枝落叶含有丰富的酚,分解缓慢,随着有机质表土层的形成,养分存储于有机养分库中,主要由具有石南状根的植物所吸收利用。黑果岩高兰(Empetr... 详细信息

本文回顾了关于北欧地区岩高兰(Empetrum nigrum ***和***)生态系统的知识。因为岩高兰叶片及其枯枝落叶含有丰富的酚,分解缓慢,随着有机质表土层的形成,养分存储于有机养分库中,主要由具有石南状根的植物所吸收利用。黑果岩高兰(Empetrum nigrum)亚种Hermaphroditum是强有力的养分竞争者,并且在演替后期能战胜多数植物。这是化学干扰(他感作用)和资源竞争所致。岩高兰作为一种有机体耐大气污染,在适林海岸石南丛生地,由于大气中大量氮的沉积其生长活力甚至有所增加,但是它对机械干扰及火烧非常敏感。然而,有迹象表明,空气中无机气氮的输入可对岩高兰占优势时所形成的封闭式营养循环产生干扰。

关键词：北欧岩高兰生态系统功能环境变化敏感性

An overview of cryptographic primitives for possible use in 5G and beyond

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Science China(Information Sciences) 2020年第12期63卷 5-26页

作者： Jing YANG Thomas johansson Department of Electrical and Information Technology Lund University

This survey overviews the potential use of cryptographic primitives in the fifth-generation mobile communications system(aka 5G) and beyond. It discusses the new security challenges that come with 5G and presents the upcoming security architecture. It shows the use of current cryptographic algorithms and discusses new algorithms or modifications of existing ones, that can be relevant. It also discusses the need for lightweight algorithms to meet the new use cases as well as the general demand for algorithms secure even when large quantum computers are available.

关键词： 5G cryptographic primitives lightweight cryptography post-quantum cryptography

Biomass production of hybrid aspen growing on former farm land in Sweden

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Journal of Forestry Research 2013年第2期24卷 237-246页

作者： Tord johansson Department of Energy and Technology Swedish University of Agricultural Sciences

We construct dry weight equations for hybrid aspen growing on former farmland in Sweden. Dry weight equations for fractions of hybrid aspen trees were also made. We estimated biomass production in 24 stands. The stands were located in Sweden at latitudes ranging from 55 to 60o N. The mean age was 18 years （range 15-23）, the mean stand density 1090 stems·ha-1 （range 378 2374）, and the mean diameter at breast height （over bark） 178 mm （range 85 244 mm）. Soil types in the hybrid aspen stands were mainly clay （21 stands）, tills （2 stands） and other （1 stand）. The mean total standing dry weight above stump level （≈ 200 mm） for the hybrid aspen stands was 135±53 t·ha-1 with a range of 42 219 t·ha-1 . In addition to estimating conventional dry weights of trees and tree components, basic density, specific leaf area （SLA）, projected leaf area （PLA） and leaf area index （LAI） were estimated and were in agreement with published figures.

关键词： basic density biomass production farmland hybrid aspen MAI plantation forestry

A site dependent top height growth model for hybrid aspen

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Journal of Forestry Research 2013年第4期24卷 691-698页

作者： Tord johansson Department of Energy and Technology Swedish University of Agricul- tural Sciences

In this study height growth models for hybrid aspen were developed using three growth equations. The mean age of the hybrid aspen was 21 years （range 15-51 years） with a mean stand density of 946 stems ha-~ （87-2374） and a mean diameter at breast height （over bark） of 19.6 cm （8.5-40.8 cm）. Site index was also examined in relation to soil type. Multiple samples were collected for three types of soil： light clay, medium clay and till. Site index curves were constructed using the col- lected data and compared with published reports. A number of dynamic equations were assessed for modeling top-height growth from total age.

关键词： top height farmland hybrid aspen site index soil types stands total age soil type

Misconceptions in global reactions and formula writing

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Defence Technology（防务技术） 2016年第5期12卷 419-421页

作者： Stig R. johansson The Swedish Section for Detonics and Combustion Sweden

The frequently used concept of "global reaction" is discussed and the reason for the confusion behind explained. The misconception is cleared by formula writing based on the donor–acceptor(donac) reaction concept and... 详细信息

关键词： Global reaction Donac reactions Formula writing Pyrotechnics Chlorate manufacture

Rock mass response for lined rock caverns subjected to high internal gas pressure

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Journal of Rock Mechanics and Geotechnical Engineering 2023年第1期15卷 119-129页

作者： Davi Rodrigues Damasceno Johan Spross Fredrik johansson Division of Soil and Rock Mechanics KTH Royal Institute of TechnologySE-10044StockholmSweden

The storage of hydrogen gas in underground lined rock caverns(LRCs)enables the implementation of the first fossil-free steelmaking process to meet the large demand for crude *** the response of rock mass is important to ensure that gas leakage due to rupture of the steel lining does not *** and numerical models can be used to estimate the rock mass response to high internal pressure;however,the fitness of these models under different in situ stress conditions and cavern shapes has not been *** this paper,the suitability of analytical and numerical models to estimate the maximum cavern wall tangential strain under high internal pressure is *** analytical model is derived in detail and finite element(FE)models considering both two-dimensional(2D)and three-dimensional(3D)geometries are *** models are verified with field measurements from the LRC in Skallen,southwestern *** analytical model is inexpensive to implement and gives good results for isotropic in situ stress conditions and large cavern *** the case of anisotropic horizontal in situ stresses,as the conditions in Skallen,the 3D FE model is the best approach.

关键词： Lined rock caverns(LRCs) High pressure Rock mass response In situ stress condition Cavern shape Gas storage

Effect of rock joints on lined rock caverns subjected to high internal gaspressure

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Journal of Rock Mechanics and Geotechnical Engineering 2023年第7期15卷 1625-1635页

作者： Davi Rodrigues Damasceno Johan Spross Fredrik johansson Division of Soil and Rock Mechanics KTH Royal Institute of TechnologySE-10044StockholmSweden

The storage of hydrogen gas in lined rock caverns(LRCs)may enable the implementation of the firstlarge-scale fossil-free steelmaking process in Sweden,but filling such storage causes joints in the rockmass to open,concentrating strains in the *** structural interaction between the LRC componentsmust be able to reduce the strain concentration in the sealing steel lining;however,this interaction iscomplex and difficult to predict with analytical *** this paper,the strain concentration in LRCsfrom the opening of rock joints is studied using finite element(FE)analyses,where the large-and small-scale deformation behaviors of the LRC are *** model also includes concrete crack initiation anddevelopment with increasing gas pressure and rock joint *** interaction between the jointed rockmass and the reinforced concrete,the sliding layer,and the steel lining is *** results showthat the rock mass quality and the spacing of the rock joints have the greatest influence on the straindistributions in the steel *** largest effect of rock joints on the maximum strains in the steellining was observed for geological conditions of“good”quality rock masses.

关键词： Lined rock cavern(LRC) Rock joints Strain concentrations Lining interaction Finite element(FE)analysis High gas pressure