A micromechanics-enhanced finite element formulation for modelling heterogeneous materials

In the analysis of composite materials with heterogeneous microstructures, full resolution of the heterogeneities using classical numerical approaches can be computationally prohibitive. This paper presents a micromechanics-enhanced finite element formulation that accurately captures the mechanical behaviour of heterogeneous materials in a computationally efficient manner. The strategy exploits analytical solutions derived by Eshelby for ellipsoidal inclusions in order to determine the mechanical perturbation fields as a result of the underlying heterogeneities. Approximation functions for these perturbation fields are then incorporated into a finite element formulation to augment those of the macroscopic fields. A significant feature of this approach is that the finite element mesh does not explicitly resolve the heterogeneities and that no additional degrees of freedom are introduced. In this paper, hybrid-Trefftz stress finite elements are utilised and performance of the proposed formulation is demonstrated with numerical examples. The method is restricted here to elastic particulate composites with ellipsoidal inclusions but it has been designed to be extensible to a wider class of materials comprising arbitrary shaped inclusions.Comment: 28 pages, 12 figures, 2 table

27P Chirurgiczne leczenie powikłań powstałych w wyniku radioterapii nowotworów dróg rodnych i jąder

Jednym z elementów leczenia dróg rodnych i jąder jest radioterapia. W wyniku tego postępowania może dojść do uszkodzenia promieniami innych narządów. Szczególną wrażliwość wykazuje jelito cienkie oraz jelito grube. Na skutek popromiennego zapalenia jelit występują krwawienia do światła jelita, perforacje, pojawiają się zrosty i zwężenia prowadzące do niedrożności przewodu pokarmowego. Niedrożność może być też spowodowana atonią odcinków uszkodzonego jelita. Częstym powikłaniem popromiennym jest przetoka pochwowo- odbytnicza. W takich przypadkach konieczne jest leczenia operacyjne.Celem pracy jest ocena leczenia chirurgicznego powikłań popromiennych. W Oddziale Chirurgii I WCO w latach 1988–1998 z powodu powikłań popromiennych leczono 90 chorych w wieku 31 do 73 lat; 3 mężczyzn i 87 kobiet. Z rozpoznaniem Ca. colli uteri 79 Ca. endometri 6, Ca. ovariorum 2 kobiety, 3 mężczyzn z rozpoznaniem Ca testis.54 operowano z powodu przetoki pochwowoodbytniczej. 15 razy z powodu krwawienia do świateł jelita, przyczyną 20 operacji była niedrożność przewodu pokarmowego, 1 raz perforacja jelita.Metodę leczenia dostosowywano indywidualnie do poszczególnych przypadków. Stosowano chirurgiczne wywołanie odbytu na esicy lub poprzecznicy, wykonywano operacje Hartmana lub brzuszno-kroczowe odjęcie odbytnicy, stosowano odcinkowe resekcje jelita lub zespolenia omijające, podwiązywano naczynia biodrowe wewnętrzne. W ostatnim okresie w przypadkach krwawienia z odbytnicy z powodzeniem stosowano laseroterapię aparatem Nd: YAG. Należy zaznaczyć, że wymienione zabiegi operacyjne wykonywane były w trudnych warunkach spowodowanych uszkodzeniami popromiennymi; jelito o słabej ścianie wrażliwe na urazy, liczne zrosty oraz krótka zmieniona zapalnie krezka jelita. Niejednokrotnie dużym problemem decyzyjnym i diagnostycznym jest zróżnicowanie niedrożności popromiennej z niedrożnością spowodowaną rozsiewem procesu nowotworowego. Chorzy są w złym stanie ogólnym, a obraz kliniczny jest niejasny. Postępowanie w takich przypadkach wymaga pewnego doświadczenia w prowadzeniu chorych leczonych promieniami.Wnioski1.Metody chirurgicznego leczenia powikłań popro miennych muszą być dostosowane indywidualnie do każdego przypadku.2.Leczenie operacyjne pomimo trudności i ryzyka jest celowe i daje dobre efekty terapeutyczne.3.W przypadku krwawienia z odbytnicy uszkodzonej promieniami nową skuteczną metodą leczenia jest laseroterapia

Unconventional superconducting phases in a correlated two-dimensional Fermi gas of nonstandard quasiparticles: a simple model

We discuss a detailed phase diagram and other microscopic characteristics on the applied magnetic field - temperature (H_a-T) plane for a simple model of correlated fluid represented by a two-dimensional (2D) gas of heavy quasiparticles with masses dependent on the spin direction and the effective field generated by the electron correlations. The consecutive transitions between the Bardeen-Cooper-Schrieffer (BCS) and the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phases are either continuous or discontinuous, depending on the values of H_a and T. In the latter case, weak metamagnetic transitions occur at the BCS-FFLO boundary. We single out two different FFLO phases, as well as a reentrant behaviour of one of them at high fields. The results are compared with those for ordinary Landau quasiparticles in order to demonstrate the robustness of the FFLO states against the BCS state for the case with spin-dependent masses (SDM). We believe that the mechanism of FFLO stabilization by SDM is generic: other high-field low-temperature (HFLT) superconducting phases benefit from SDM as well.Comment: 10 pages, 4 figure

Measurements of Gas Pressure into the MV Arc Plasma Environment

Current interrupters equipped with arc quenching system based on combination of forced air flow and gassing material were the object of the research described in this paper. Arc quenching gas pressure inside the extinguishing chamber in direct vicinity of plasma arc was recorded by means of developed measurement system resistant for heavy duty conditions existent inside the chamber during breaking. Gas pressure was estimated for several values of load current at 12/24 kV source voltage

Foreign direct investments and the dynamics of trade and capital flows: Schumpeterian insights for sustained development

This article analyses the role of foreign direct investment (FDI) in trade and development theory and outlines the resulting implications for economic policy. We propose an alternative model of international trade and development based on absolute, not comparative advantages of firms, which are nested in countries but compete internationally. Applying a Schumpeterian theory of dynamic development, we consider how firms can either increase their competitiveness through productivity gains at a given wage level, or by combining the existing high level of productivity with lower wages in low-income countries. We argue that the aim of competition policy must be to improve the quality of economic competition in international markets, limit monopoly rents and disincentivise rent-seeking activities through the mere outsourcing of production. To that end, we propose that economic policy must reinstate rigorous wage bargaining regimes and make FDI subject to wage conditionality, obliging foreign companies to increase their wages in the host economy in line with average national productivity growth and the national inflation target

Multi-scale finite element based time-dependent reliability analysis for laminated fibre reinforced composites.

No abstract available

Stochastic multi-scale finite element based reliability analysis for laminated composite structures

This paper proposes a novel multi-scale approach for the reliability analysis of composite structures that accounts for both microscopic and macroscopic uncertainties, such as constituent material properties and ply angle. The stochastic structural responses, which establish the relationship between structural responses and random variables, are achieved using a stochastic multi-scale finite element method, which integrates computational homogenisation with the stochastic finite element method. This is further combined with the first- and second-order reliability methods to create a unique reliability analysis framework. To assess this approach, the deterministic computational homogenisation method is combined with the Monte Carlo method as an alternative reliability method. Numerical examples are used to demonstrate the capability of the proposed method in measuring the safety of composite structures. The paper shows that it provides estimates very close to those from Monte Carlo method, but is significantly more efficient in terms of computational time. It is advocated that this new method can be a fundamental element in the development of stochastic multi-scale design methods for composite structures

Preconditioning Stimulus Intensity Alters Paired-Pulse TMS Evoked Potentials.

Motor cortex (M1) paired-pulse TMS (ppTMS) probes excitatory and inhibitory intracortical dynamics by measurement of motor-evoked potentials (MEPs). However, MEPs reflect cortical and spinal excitabilities and therefore cannot isolate cortical function. Concurrent TMS-EEG has the ability to measure cortical function, while limiting peripheral confounds; TMS stimulates M1, whilst EEG acts as the readout: the TMS-evoked potential (TEP). Whilst varying preconditioning stimulus intensity influences intracortical inhibition measured by MEPs, the effects on TEPs is undefined. TMS was delivered to the left M1 using single-pulse and three, ppTMS paradigms, each using a different preconditioning stimulus: 70%, 80% or 90% of resting motor threshold. Corticospinal inhibition was present in all three ppTMS conditions. ppTMS TEP peaks were reduced predominantly under the ppTMS 70 protocol but less so for ppTMS 80 and not at all for ppTMS 90. There was a significant negative correlation between MEPs and N45 TEP peak for ppTMS 70 reaching statistical trends for ppTMS 80 and 90. Whilst ppTMS MEPs show inhibition across a range of preconditioning stimulus intensities, ppTMS TEPs do not. TEPs after M1 ppTMS vary as a function of preconditioning stimulus intensity: smaller preconditioning stimulus intensities result in better discriminability between conditioned and unconditioned TEPs. We recommend that preconditioning stimulus intensity should be minimized when using ppTMS to probe intracortical inhibition

Preconditioning stimulus intensity alters paired‐pulse tms evoked potentials

Motor cortex (M1) paired‐pulse TMS (ppTMS) probes excitatory and inhibitory intracor-tical dynamics by measurement of motor‐evoked potentials (MEPs). However, MEPs reflect cortical and spinal excitabilities and therefore cannot isolate cortical function. Concurrent TMS‐EEG has the ability to measure cortical function, while limiting peripheral confounds; TMS stimulates M1, whilst EEG acts as the readout: the TMS‐evoked potential (TEP). Whilst varying preconditioning stimulus intensity influences intracortical inhibition measured by MEPs, the effects on TEPs is undefined. TMS was delivered to the left M1 using single‐pulse and three, ppTMS paradigms, each using a different preconditioning stimulus: 70%, 80% or 90% of resting motor threshold. Corticospinal inhibition was present in all three ppTMS conditions. ppTMS TEP peaks were reduced predominantly under the ppTMS 70 protocol but less so for ppTMS 80 and not at all for ppTMS 90. There was a significant negative correlation between MEPs and N45 TEP peak for ppTMS 70 reaching statistical trends for ppTMS 80 and 90. Whilst ppTMS MEPs show inhibition across a range of preconditioning stimulus intensities, ppTMS TEPs do not. TEPs after M1 ppTMS vary as a function of preconditioning stimulus intensity: smaller preconditioning stimulus intensities result in better discriminability between conditioned and unconditioned TEPs. We recommend that preconditioning stimulus intensity should be minimized when using ppTMS to probe intracortical inhibition

Modelling of thermal behaviour of iron oxide layers on boiler tubes

Slender boiler tubes are subject to localised swelling when they are expose to excessive heat. The latter is due to the formation of an oxide layer, which acts as an insulation barrier. This excessive heat can lead to microstructural changes in the material that would reduce the mechanical strength and would eventually lead to critical and catastrophic failure. Detecting such creep damage remains a formidable challenge for boiler operators. It involves a costly process of shutting down the plant, performing electromagnetic and ultrasonic non-destructive inspection, repairing or replacing damaged tubes and finally restarting the plant to resume its service. This research explores through a model developed using a finite element computer simulation platform the thermal behaviour of slender tubes under constant temperature exceeding 723 \K. Our simulation results demonstrate that hematite layers up to 15 \μm thickness inside the tubes do not act as insulation. They clearly show the process of long term overheating on the outside of boiler tubes which in turn leads to initiation of flaws