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A new analytical model for thermal stresses in multi-phase materials and lifetime prediction methods

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Acta Mechanica Sinica 2008年第2期24卷 189-206页

作者： ladislav Ceniga Institute of Materials Research Slovak Academy of Sciences Watsonova 47 04353 Koice Slovak Republic

Based on the fundamental equations of the mechanics of solid continuum, the paper employs an analytical model for determination of elastic thermal stresses in isotropic continuum represented by periodically distributed spherical particles with different distributions in an infinite matrix, imaginarily divided into identical cells with dimensions equal to inter-particle distances, containing a central spherical particle with or without a spherical envelope on the particle surface. Consequently, the multi-particle-（envelope）- matrix system, as a model system regarding the analytical modelling, is applicable to four types of multi-phase materials. As functions of the particle volume fraction v, the inter-particle distances dl, d2, d3 along three mutually per- pendicular axes, and the particle and envelope radii, R1 and R2, respectively, the thermal stresses within the cell, are originated during a cooling process as a consequence of the difference in thermal expansion coefficients of phases rep- resented by the matrix, envelope and particle. Analytical-（experimental）-computational lifetime prediction methods for multi-phase materials are proposed, which can be used in engineering with appropriate values of parameters of real multi-phase materials.

关键词： Thermal stress Multi-phase material Lifetime prediction Analytical modelling

Thermal-stress induced phenomena in two-component material:part I

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Acta Mechanica Sinica 2009年第6期25卷 811-820页

作者： ladislav Ceniga Institute of Materials Research Slovak Academy of SciencesWatsonova 47 040 01 KosiceSlovak Republic

The paper deals with analytical fracture mechanics to consider elastic thermal stresses acting in an isotropic multi-particle-matrix system. The multi-particle-matrix system consists of periodically distributed spherical particles in an infinite matrix. The thermal stresses originate during a cooling process as a consequence of the difference αm - αp in thermal expansion coefficients between the matrix and the particle, αm and αp, respectively. The multi-particle-matrix system thus represents a model system applicable to a real two-component material of a precipitation-matrix type. The infinite matrix is imaginarily divided into identical cubic cells. Each of the cubic cells with the dimension d contains a central spherical particle with the radius R, where d thus corresponds to inter-particle distance. The parameters R, d along with the particle volume fraction v = v（R, d） as a function of R, d represent microstructural characteristics of a twocomponent material. The thermal stresses are investigated within the cubic cell, and accordingly are functions of the microstructural characteristics. The analytical fracture mechanics includes an analytical analysis of the crack initiation and consequently the crack propagation both considered for the spherical particle （q = p） and the cell matrix （q = m）. The analytical analysis is based on the determination of the curve integral Wcq of the thermal-stress induced elastic energy density Wq. The crack initiation is represented by the determination of the critical particle radius Rqc = Rqc（V）. Formulae for Rqc are valid for any two-component mate- rial of a precipitate-matrix type. The crack propagation for R 〉 Rqc is represented by the determination of the function fq describing a shape of the crack in a plane perpendicular

关键词： Thermal stress . Limit state .Analytical modelling .Two-component material

Thermal stresses in two-and three-component anisotropic materials

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Acta Mechanica Sinica 2010年第5期26卷 695-709页

作者： ladislav Ceniga Institute of Materials Research Slovak Academy of Sciences

This paper deals with an analytical model of thermal stresses which originate during a cooling process of an anisotropic solid continuum with uniaxial or triaxial anisotropy. The anisotropic solid continuum consists of anisotropic spherical particles periodically distributed in an anisotropic infinite matrix. The particles are or are not embedded in an anisotropic spherical envelope, and the infinite matrix is imaginarily divided into identical cubic cells with central particles. The thermal stresses are thus investigated within the cubic cell. This mulfi-particle-（envelope）-matrix system based on the cell model is applicable to two- and three-component materials of precipitate-matrix and precipitate-envelope-matrix types, respectively. Finally, an analysis of the determination of the thermal stresses in the multi-par- ticle-（envelope）-matrix system which consists of isotropic as well as uniaxial- and/or triaxial-anisotropic components is presented. Additionally, the thermal-stress induced elastic energy density for the anisotropic components is also derived. These analytical models which are valid for isotropic, anisotropic and isotropic-anisotropic multi-particle- （envelope）-matrix systems represent the determination of important material characteristics. This analytical determination includes：（1） the determination of a critical particle radius which defines a limit state regarding the crack initiation in an elastic, elastic-plastic and plastic components; （2） the determination of dimensions and a shape of a crack propagated in a ceramic components; （3） the determination of an energy barrier and micro-/macro-strengthening in a component; and （4） analytical-（experimental）-computational methods of the lifetime prediction. The determination of the thermal stresses in the anisotropic components presented in this paper can be used to determine these material characteristics of real two- and three-component materials with anisotropic components or with anisotropic and

关键词： Thermal stress Component material Anisotropic solid continuum Analytical modelling Cell model

Thermal-stress induced phenomena in two-component material:Part Ⅱ

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Acta Mechanica Sinica 2010年第1期26卷 101-106页

作者： ladislav Ceniga Institute of Materials Research Slovak Academy of SciencesWatsonova 47040 01 KosiceSlovak Republic

The paper deals with analytical models of the elastic energy gradient Wsq representing an energy barrier. The energy barrier is a surface integral of the elastic energy density Wq. The elastic energy density is induced by thermal stresses acting in an isotropic spherical particle （q = p） with the radius R and in a cubic cell of an isotropic matrix （q = m）. The spherical particle and the matrix are components of a multi-particle-matrix system representing a model system applicable to a real two-component material of a precipitation-matrix type. The multi-particle-matrix system thus consists of periodically distributed isotropic spherical particles and an isotropic infinite matrix. The infinite matrix is imaginarily divided into identical cubic cells with a central spherical particle in each of the cubic cells. The dimension d of the cubic cell then corresponds to an inter-particle distance. The parameters R, d along with the particle volume fraction v = v（R, d） as a function of R, d represent micro- structural characteristics of a real two-component material. The thermal stresses are investigated within the cubic cell, and accordingly are functions of the microstructural charac- teristics. The thermal stresses originate during a cooling pro- cess as a consequence of the difference am - ap in thermal expansion coefficients between the matrix and the particle, am and ap, respectively. The energy barrier Wsq is used for the determination of the thermal-stress induced strengthening aq. The strengthening represents resistance against com- pressive or tensile mechanical loading for am - ap 〉 0 or am - ap 〈 0. respectively.

关键词： Thermal stress Strengthening Analyticalmodelling Two-component material

Clinical outcomes of radiofrequency catheter ablation of atrial fibrillation in octogenarians lO-year experience of a one high-volume center

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Journal of Geriatric Cardiology 2017年第9期14卷 575-581页

作者： Alan Bulava Jiri Hanis ladislav Dusek Department of Cardiology Ceske Budejovice Hospital Ceske Budejovice Czech Republic Faculty of Medicine and Dentistry Palacky University Olomouc Czech Republic Faculty of Health and Social Sciences University of South Bohemia in Ceske Budejovice Czech Republic Institute of Biostatistics and Analyses Faculty of Medicine Masaryk University Brno Czech Republic

Background Prevalence of atrial fibrillation （AF） increases with age. Radiofrequency catheter ablation （RFCA） is an establishedtreatment option superior to antiarrhythmics （AAs）. In this study, we investigated safety and efficacy of RFCA of AF in *** From our database, we extracted procedural and follow-up data for patients 〉 80 years with symptomatic AF undergoing RFCAand compared this population to RFCA patients 〈 50 years. All patients underwent pulmonary vein isolation （PVI） supplemented by linearlesions in PVI-nonresponders. Arrhythmia-free survival was assessed using seven day Holter every three months post procedure. All patientscompleted their 12 months follow-up. Results Fifty patients aged ≥80 years （80.5 ± 1.6 years） were compared to 259 patients aged 〈 50years （43.5±5.5 years）. The RFCA complication rate did not vary between groups. No differences in procedural characteristics were seenafter being analyzed by type of AF. Among patients with paroxysmal AF, 71.4% octogenarian vs. 84.7% young patients was free of anyarrhythmia, without AAs, after single procedure. For non-paroxysmal AF, arrhythmia-free survival without AAs, was considerably lower（58.6% octogenarians vs. 81.2% younger patients, P = 0.023）. If AAs were used, arrhythmia-free survival for paroxysmal AF increased to90.5% and 92.1% in octogenarians and younger patients, respectively; and in non-paroxysmal AF it increased to 79.3% vs. 88.4%. ConclusionsRFCA is a safe and effective strategy to achieve normal sinus rhythm in a highly selected group of octogenarians. Paroxysmal AF ablation inoctogenarians has similar clinical effectiveness as that seen in much younger patients. Non-paroxysmal AF ablation has lower, but still rea-sonable clinical effectiveness.

关键词： Atrial fibrillation Catheter ablation Effectiveness Octogenarians Safety The elderly

On the role of stablecoins in cryptoasset pricing dynamics

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Financial Innovation 2022年第1期8卷 975-1000页

作者： ladislav Kristoufek Institute of Economic Studies Faculty of Social SciencesCharles UniversityPragueCzech Republic Institute of Infor-mation Theory and Automation The Czech Academy of SciencesPragueCzech Republic.

We examine the interactions between stablecoins,Bitcoin,and a basket of altcoins to uncover whether stablecoins represent the investors’demand for trading and investing into cryptoassets or rather play a role as boosting mechanisms during cryptomarkets price *** a set of instruments covering the standard cointegration framework as well as quantile-specific and non-linear causality tests,we argue that stablecoins mostly reflect an increasing demand for investing in cryptoassets rather than serve as a boosting mechanism for periods of extreme *** further discuss some specificities of 2017,even though the dynamic patterns remain very similar to the general ***,we do not find support for claims about stablecoins being bubble boosters in the cryptoassets ecosystem.

关键词： Cryptocurrencies Cryptoassets Bitcoin Stablecoins Tether

Is there a potential of circulating miRNAs as biomarkers in rheumatic diseases?

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Genes & Diseases 2023年第4期10卷 1263-1278页

作者： Klára Prajzlerová ladislav Senolt Mária Filková Institute of Rheumatology Prague 12800Czech Republic Department of Rheumatology First Faculty of MedicineCharles UniversityPrague 12800Czech Republic

t MicroRNAs(miRNAs)are small non-coding single-stranded RNAs of about 22 nucle-otides in length that act as post-transcriptional regulators of gene *** on the complementarity between miRNA and target mRNA,cleavage,destabilization,or transla-tional suppression of mRNA occurs within the RISC(RNA-induced silencing complex).As gene expression regulators,miRNAs are involved in a variety of biological *** of miRNAs and their target genes contribute to the pathophysiology of many diseases,including autoimmune and inflammatory *** are also present extracellularly in their sta-ble form in body *** incorporation into membrane vesicles or protein complexes with Ago2,HDL,or nucleophosmin 1 protects them against ***-free miRNAs can be deliv-ered to another cell in vitro and maintain their functional ***,miRNAs can be considered mediators of intercellular *** remarkable stability of cell-free miRNAs and their accessibility in body fluid makes them potential diagnostic or prognostic bio-markers and potential therapeutic *** we provide an overview of the potential role of circulating miRNAs as biomarkers of disease activity,therapeutic response,or diagnosis in rheumatic *** circulating miRNAs reflect their involvement in the pathogenesis,while for plenty,their pathogenetic mechanisms remain to be *** miRNAs described as biomarkers were also shown to be of therapeutic potential,and some miRNAs arealready tested in clinical trials.

关键词： Biomarker Diagnosis miRNA Rheumatic diseases Therapy

Laser Cladding of Cold-Work Tool Steel by Pulse Shaping

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Journal of Materials Science & Technology 2011年第8期27卷 707-713页

作者： Matej Pleterski Janez Tuek Tadej Muhic ladislav Kosec Faculty of Mechanical Engineering University of Ljubljana Akereva cesta 6 TKC D.O.O. Trnovska Ulica 8 Faculty of Natural Sciences and Engineering University of Ljubljana Akereva Cesta 12

Repair welding of cold-work tool steels in cold is very risky and almost impossible by conventional processes. The application of pulse shaping in laser cladding with wire to avoid the solidification problems in relevant steel is demonstrated. The results show that sound remelting and/or cladding can be achieved by the right selection of laser parameters and pulse shape, i.e. long pulse duration, moderate pulse peak powers and ramped-down pulse shape. Despite the defects and softening in the cladding due to the formation of retained austenite, the cladding shows better wear resistance at lower loads compared to the heat-treated base material.

关键词： Laser cladding Repair welding Tool steel Wear test

Beyond direct neighbourhood effects: higher-order interactions improve modelling and predicting tree survival and growth

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National Science Review 2021年第5期8卷 38-47页

作者： Yuanzhi Li Margaret M.Mayfield Bin Wang Junli Xiao Kamil Kral David Janik Jan holik Chengjin Chu Department of Ecology State Key Laboratory of BiocontrolSchool of Life SciencesSun Yat-sen University Guangxi Key Laboratory of Plant Conservation and Restoration Ecology in Karst Terrain Guangxi Institute of BotanyGuangxi Zhuang Autonomous Region and Chinese Academy of Sciences Department of Silviculture Faculty of Forestry and Wood TechnologyMendel University in Brno School of Biological Sciences The University of Queensland Department of Forest Ecology Silva Tarouca Research Institute

It is known that biotic interactions are the key to species coexistence and maintenance of species *** studies focus overwhelmingly on pairwise interactions between organisms, ignoring complex higher-order interactions(HOIs). In this study, we present a novel method of calculating individual-level HOIs for trees, and use this method to test the importance of size-and distance-dependent individual-level HOIs to tree performance in a 25-ha temperate forest dynamic plot. We found that full HOI-inclusive models improved our ability to model and predict the survival and growth of trees, providing empirical evidence that HOIs strongly influence tree performance in this temperate forest. Specifically, assessed HOIs mitigate the competitive direct effects of neighbours on survival and growth of focal trees. Our study lays a foundation for future investigations of the prevalence and relative importance of HOIs in global forests and their impact on species diversity.

关键词： pairwise interactions indirect interactions density-dependent size- and distance-dependent Zofin Forest Dynamic Plot