Discrete and phase field methods for linear elastic fracture mechanics: a comparative study and state-of-the-art review

© 2019 by the authors. Three alternative approaches, namely the extended/generalized finite element method (XFEM/GFEM), the scaled boundary finite element method (SBFEM) and phase field methods, are surveyed and compared in the context of linear elastic fracture mechanics (LEFM). The purpose of the study is to provide a critical literature review, emphasizing on the mathematical, conceptual and implementation particularities that lead to the specific advantages and disadvantages of each method, as well as to offer numerical examples that help illustrate these features

Adaptive isogeometric analysis for phase‐field modeling of anisotropic brittle fracture

The surface energy a phase‐field approach to brittle fracture in anisotropic materials is also anisotropic and gives rise to second‐order gradients in the phase field entering the energy functional. This necessitates C 1 continuity of the basis functions which are used to interpolate the phase field. The basis functions which are employed in isogeometric analysis (IGA), such as nonuniform rational B‐splines and T‐splines naturally possess a higher order continuity and are therefore ideally suited for phase‐field models which are equipped with an anisotropic surface energy. Moreover, the high accuracy of spline discretizations, also relative to their computational demand, significantly reduces the fineness of the required discretization. This holds a fortiori if adaptivity is included. Herein, we present two adaptive refinement schemes in IGA, namely, adaptive local refinement and adaptive hierarchical refinement, for phase‐field simulations of anisotropic brittle fracture. The refinement is carried out using a subdivision operator and exploits the Bézier extraction operator. Illustrative examples are included, which show that the method can simulate highly complex crack patterns such as zigzag crack propagation. An excellent agreement is obtained between the solutions from global refinement and adaptive refinement, with a reasonable reduction of the computational effort when using adaptivity

Exploring entrepreneurial conceptions, beliefs and intentions of Greek graduates

Purpose – The purpose of this paper is to identify entrepreneurial conceptions and beliefs of Greek graduates, comparing science and economics graduates and nascent entrepreneurs to general population samples. Differences in conceptions are further examined as determinants of entrepreneurial intention. Design/methodology/approach – The paper utilizes a 34-item questionnaire for a graduates’ survey in a science and an economics department (n=413). The questions concern five major subjects of entrepreneurial thinking: conceptualizing entrepreneurship, entrepreneurial success factors, motivation, risk management and business financing. Entrepreneurial intention is identified through a six-item scale. Structural equation model is used to retrieve an explanatory pattern for the present variables and data. Findings – Greek science and economics graduates typically exhibit differences in beliefs that downsize through entrepreneurship education. Entrepreneurial nascence is supported by personal competencies, self-confidence, planning capacities and adoption of an entrepreneurial style. Beyond expected dependencies on personal entrepreneurial competencies, motives, organizational skills and other subjective beliefs, possible misapprehension of entrepreneurial notions were found to reduce the entrepreneurial intention. The latter result differentiates nascent entrepreneurs from latent ones. Research limitations/implications – Limitations concern the full representation of Greek universities, the representation of science disciplines and the exhaustive representation of the spectrum of beliefs associated with business venturing. Practical implications – Findings have direct implications for entrepreneurship education and educational policies. This is because beliefs are cognitive structures which can be altered through effective education and counseling methods. Social implications – Findings reflect socio-economic influences on young potential entrepreneurs in Greece during the debt crisis. Originality/value – The paper originally contributes to the survey of entrepreneurial beliefs in Greece. Beliefs are thought culture and field of study specific, and thus, the paper not only covers a gap in literature for the Greek population, but also adds comparative analyses between: science/economics graduates and the nascent entrepreneurs/general population. In this way, it seeks the origin of different beliefs and also attempts a consistent examination of their relations into relevant conceptualizations as determinants of entrepreneurial intention. Comparisons between economics and science students are scarce in the literature offering insights toward the interdisciplinary fostering of entrepreneurial mindsets. © 2016, © Emerald Group Publishing Limited

On steady shell formation in stellar atmospheres

The energy balance of the analytical solutions of Kakouris & Moussas ([CITE]) for a steady state of an externally heated/cooled 2-D circumstellar envelope is investigated. It is found that the required heating/cooling rates are physically realistic and can be related to specific microscopic mechanisms. We find that in the subsonic region of the wind the fluid is mechanically heated. In the supersonic stellar envelope the fluid is cooled at a rate which is consistent with radiative cooling to space. The energy balance of steady shell or blob formation in the envelopes of luminous early or late type supergiants is also investigated (Kakouris & Moussas [CITE]). We find that radiative cooling occurs in the intermediate deceleration region of the three-zone envelope. Indicative of the local thermodynamic processes is the effective polytropic index α which takes values close to the star between 1 and 4, becoming $\simeq$2 at larger distances. The heated subsonic region close to the stellar surface is isothermal and becomes adiabatic at the sonic transition. We find that the polytropic index α is less than unity in the vicinity of the dense blob, indicating that the region may be dominated by convection

On steady shell formation in stellar atmospheres II. Energy balance in a non-polytropic stellar envelope

The energy balance of the analytical solutions of Kakouris & Moussas (1997) for a steady state of an externally heated/cooled 2-D circumstellar envelope is investigated. It is found that the required heating/cooling rates are physically realistic and can be related to specific microscopic mechanisms. We find that in the subsonic region of the wind the fluid is mechanically heated. In the supersonic stellar envelope the fluid is cooled at a rate which is consistent with radiative cooling to space. The energy balance of steady shell or blob formation in the envelopes of luminous early or late type supergiants is also investigated (Kakouris & Moussas 1998). We find that radiative cooling occurs in the intermediate deceleration region of the three-zone envelope. Indicative of the local thermodynamic processes is the effective polytropic index α which takes values close to the star between 1 and 4, becoming ≃2 at larger distances. The heated subsonic region close to the stellar surface is isothermal and becomes adiabatic at the sonic transition. We find that the polytropic index α is less than unity in the vicinity of the dense blob, indicating that the region may be dominated by convection

Entrepreneurship pedagogies in lifelong learning: Emergence of criticality?

The present paper aims to address an instructional perspective for entrepreneurship courses introduced to lifelong learners. The new approach combines critical thinking with experiential learning in a common framework able to facilitate entrepreneurship education for various heterogeneous populations through lifelong learning or vocational training. The proposed approach utilizes critical instruction embedded in experiential learning as to resolve possible disorientation of learners during the common experiential/reflective instruction for entrepreneurship. A critical-thinking-deviation from Kolb's experiential learning model is introduced and preliminarily tested empirically for two different groups of adult learners. Suggested conceptualization through critical instruction is expected either to resolve disorienting situations or to lead to postponement of courses and reconsideration of the theoretical framework. The latter is due to the emancipatory nature of critical instruction and depends on both learners' intrinsic needs, assumptions and on the specific framework under which entrepreneurship education is promoted. Empirical evidence for the dual consequence, due to the adoption of critical instruction, is illustrated for the two groups of learners. The theoretical scope of the paper concerns the appropriateness and the consistency of the suggested critical-experiential teaching for entrepreneurship designed for adult learners. Implications concern entrepreneurship curricula, innovative instruction and trainers' training. © 2015 Elsevier Ltd

Образование как часть предпринимательской экосистемы

Entrepreneurial education programs are a variety of economics and management programs. In practice, we are convinced that a new approach to program development is needed, based on tight connection with entrepreneurial ecosystem. We believe that identifying the most effective approach to the development of educational programs should consider education as a part of regional entrepreneurial ecosystem. Our proposed approach to determine ways to reorganize educational programs based on the innovation theory allows us to consider the strategy for the further development of entrepreneurship education to a greater extent and increase the effectiveness of programs. In conclusion, we define the objectives of subsequent research, identifying the most interesting topics for studying the methodology of entrepreneurial education.Образовательные программы предпринимательству представляют собой подобие образовательных программ по экономике и менеджменту. Мы считаем, что необходим новый подход к разработке программ, основанный на тесной связи с предпринимательской экосистемой. Мы полагаем, что при определении наиболее эффективного подхода к разработке образовательных программ следует рассматривать образование как часть региональной предпринимательской экосистемы. Предлагаемый нами подход к определению путей реорганизации образовательных программ на основе теории инноваций позволяет нам в большей степени рассмотреть стратегию дальнейшего развития предпринимательского образования и повысить эффективность программ. В заключение мы определим задачи последующего исследования, выявив наиболее интересные темы для изучения методологии предпринимательского образования

Poly(N-hydroxypyrrole) and poly(3-phenyl-N-hydroxypyrrole):synthesis, conductivity, spectral properties and oxidation

N-Hydroxypyrrole and 3-phenyl-N-hydroxypyrrole were oxidized by (ButO2) in the presence of light to give the transient pyrrolyl-1-oxyl (nitroxide) radicals which were observed by EPR spectroscopy. The corresponding poly(N-hydroxypyrroles) were prepared by chemical oxidation with ferric salts, or, in the case of N-hydroxypyrrole only, by electrochemical oxidation in CH3CN at + 1.2 V versus SCE. The latter polymer had a considerably higher electronic conductivity than the chemically produced polymers (10-4 cf. 10-10 S cm-1), but much lower conductivity than polypyrrole prepared via the same route. It is not clear from the FT-IR spectra of these polymers whether the hydroxyl group survived intact, or whether it was converted back to the amine. Microanalyses showed that the electropolymerized materials had the expected formulation, but chemical polymerization with FeCl3 led to the introduction of one O per monomer unit in the case of pyrrole, and two and three O atoms, respectively, for FeCl3- and Fe(NO3)3-polymerized N-hydroxypyrroles. The EPR spectrum of each polymer consisted of a single featureless band at g = 2.003. The poly(N-hydroxypyrroles) were further oxidized by PbO2 and m-chloroperbenzoic acid (MCPBA) to give polymer containing a strong band at 1720 cm-1 which may be due either to a ketone group (e.g. pyrrolidone) or possibly an oxoammonium (&gt;N+O) species. Microanalyses showed that while electropolymerized polypyrrole had been oxidized by one O atom per monomer, the chemically prepared polymers (FeCl3) had been oxidized up to the same level as the ferric nitrate-prepared polymers (i.e. from two to three O per pyrrole unit). These oxidized polymers were effectively insulators.</p