Entwicklung kontinuumskompatibler Federmodelle

Die numerische Simulation des Versagensverhaltens von Werkstoffen ist eine Problemstellung, die bis heute noch nicht vollständig gelöst ist. Neben den klassischen Kontinuumsmodellierungen wie den erweiterten Finiten Elementen werden hierfür oftmals diskrete Modelle verwendet. Diese bieten den Vorteil, dass das diskrete Phänomen des Risses durch einfaches Entfernen von diskreten Elementen modelliert werden kann, wohingegen Kontinuumsmethoden eine kontinuierliche Beschreibung des Verschiebungsfelds in der Nähe der Rissspitze erfordern. Die Zuverlässigkeit bestehender diskreter Modelle ist jedoch durch signifikante Probleme in ihrer Modellierung stark eingeschränkt. So können sie bislang in der Regel homogene, klassische Kontinua nur unter Beschränkung auf isotrope Materialien bestimmter Querkontraktionszahlen abbilden. Zudem kann die Homogenität des diskreten Modells nur gewährleistet werden, indem periodische Rechengitter verwendet oder Kontinuumselemente wie Finite Elemente in das Modell eingebaut werden. Auch plastisches Verhalten - insbesondere die reine deviatorische Natur des plastischen Fließens - kann in diesen Modellen nicht abgebildet werden. In dieser Arbeit wird ein neues, kontinuumskompatibles Federmodell für zwei- und dreidimensionale quasistatische Anwendungen entwickelt, das diesen Beschränkungen nicht unterworfen ist. Hierzu werden neue Federzellen eingeführt, die mithilfe einer Kombination aus Normalkraft- und Winkelfedern einen beliebigen konstanten Dehnungszustand bei einem homogenen Material abbilden können. Es wird gezeigt, dass dieses Modell somit in der Lage ist, für Netze aus Simplex-Zellen beliebiger Geometrie ein beliebiges homogenes Material mit anisotropen Elastizitätseigenschaften im linear-elastischen Fall zu approximieren. Sie verhalten sich damit im linear-elastischen Fall so wie die linearen Dreiecks- und Tetraederelemente, die aus der Methode der Finiten Elemente bekannt sind. In der Folge wird das zweidimensionale Federmodell um eine Modellierung für elasto-plastisches Materialverhalten mit isotroper Verfestigung erweitert und dargelegt, wie auch andere Plastizitätsformulierungen in das Federmodell integriert werden können. Bei dieser Plastizitätsmodellierung werden mithilfe des dehnungsbasierten Ansatzes der Kontinuumsplastizität die plastischen Änderungen der Federn berechnet. Es wird demonstriert, dass das entwickelte Modell - erstmals für ein diskretes Modell - in der Lage ist, auch die Volumenerhaltung der plastischen Verformung exakt abzubilden. Zusätzlich wird auf den Effekt der Lokalisierung der plastischen Dehnung in Scherbändern eingegangen. Abschließend wird eine Formulierung für die Simulation von Rissen für dieses Modell vorgestellt. Analog zu diskreten Modellen aus der Literatur werden dabei sowohl dehnungsbasierte Bruchkriterien für die Federn verwendet, die die Lage der Federn berücksichtigen, als auch solche, die unabhängig von der Orientierung der Federn sind. Es kann dabei gezeigt werden, dass dieses Rissmodell im Stande ist, in Versuchen ermittelte Risspfade zu reproduzieren, sofern ein geeignetes Bruchkriterium für die Federn gewählt wird. Auch der duktile Bruch kann mit diesem Ansatz bei Nutzung der entwickelten Plastizitätsformulierung approximiert werden. Das neu entwickelte Modell ist damit in der Lage, die erwähnten Nachteile der aus der Literatur bekannten diskreten Federmodelle zu beheben, während es zugleich in der Risssimulation, für die solche Modelle regelmäßig verwendet werden, die Pfade des Risswachstums zuverlässig vorhersagen kann.One of the major problems which are yet to be solved by means of modern numerical simulations is the simulation of the fracture process of materials. To achieve this end, both simulation techniques describing the material as a continuous system and techniques using a discrete approach are used. The advantage of the latter is the fact that in these models a crack is simply formed by removal of a discrete element, whereas the former needs a description of the displacement field in the vicinity of the crack. However, discrete models currently described in literature show severe problems. The most pressing problem is that they cannot be used for modelling arbitrary homogeneous materials in computations with aperiodic meshes. While some models are able to model some homogeneous materials, they are still limited in their choice of the material parameters. In specific, these models allow only the use of isotropic materials with a fixed Poisson's ratio. An additional problem of these models is that nonlinear phenomena of the continuous material such as plasticity cannot be modelled at all without violating constraints posed by the observation of these phenomena. For example, in the case of plastic deformation the strict deviatoric nature of the plastic flow cannot be enforced upon existing discrete models. This means that such models are so far not suitable for the fracture simulation of materials with a non-negligible plastic flow before fracture. In this work, a new discrete lattice spring model for two- and three-dimensional quasi-static applications is proposed. With this model, which is comprised of normal springs and angular springs arranged in triangular and tetrahedral cells, an arbitrary homogenous material can be approximated. Within the limits of a linear-elastic analysis, this approximation is exact for every constant strain field within each cell. It thus has in this case the same properties as constant strain triangles and constant strain tetrahedrons known from the Finite Element Method. Following the introduction of this new lattice spring model, a method of modelling elasto-plastic behaviour in this model is proposed. Using a strain-driven plasticity model, both perfect plasticity and plasticity with hardening and softening can be reproduced with this approach. By mapping the continuum plastic flow resulting from this approach to the lattice springs, the discrete nature of the model is maintained. In addition, the compliance with the deviatoric nature of the plastic flow in this approach is proven and localisation phenomena occurring in this model are discussed. Finally, the fracture modelling within the context of the proposed model is discussed. Following literature, strain-driven fracture criteria are chosen for the model. These are applied both in a directional, that is along the axes of the springs, and in a rotationally invariant version. As is shown in simulations, the right choice of the fracture criterion leads to the development of crack paths during simulations, which closely follow those observed in experiments. This is the case for both brittle fracture and ductile fracture when using the proposed plasticity formulation. It is thus justified to conclude that the proposed model can be used to solve the aforementioned problems of the discrete models in literature whilst their main advantage, that is the ability to predict crack paths with simple fracture models, is being retained

Optimierung der Sekretion von rekombinanten Proteinen aus Escherichia coli durch Analyse der Genexpression

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The Early Mother-to-Child Bond and Its Unique Prospective Contribution to Child Behavior Evaluated by Mothers and Teachers

Maternal bonding has been described as the quality of the affective tie from a mother to her infant. This early bond's mental components and its longitudinal impact on child outcome have been markedly understudied. Although most researchers assume impaired maternal bonding to have a negative impact on child development, there is a lack of prospective studies evaluating this hypothesis. Since maternal mental health problems may negatively affect both bonding quality and child development, it is still to be determined whether there is a unique contribution of bonding quality to child behavior problems over and above maternal psychopathology. We examined a community sample of 101 mother-child dyads at the child's age of 2 weeks (t1) and 6 weeks (t2), 4 months (t3), 14 months (t4), and 5.5 years (t5). Maternal bonding and psychopathology were assessed at time points t1-t4 using the Postpartum Bonding Questionnaire (PBQ-16) and the Symptom Checklist Revised (SCL 90-R). Child behavior problems were rated in a multi-informant design by mothers and teachers at t5 using the Strengths and Difficulties Questionnaire (SDQ). In the case of maternal judgment of child behavior problems, bonding at 14 months (t4) proved to be a significant predictor ((beta = 0.30;p = 0.011). Teacher-rated child behavior problems were significantly predicted by maternal bonding at 2 weeks (t1;beta = 0.48;p = 0.025). Our results indicate a prospective influence of the early mother-infant bond on child development and underline the unique contribution of bonding quality to child behavior problems over and above the impact of maternal psychopathology in a community sample. (C) 2016 S. Karger AG, Base

Amphiphilic block copolymers as stabilizers in emulsion polymerization: Effects of molecular weight dispersity and evidence of self-folding behavior

Emulsion polymerizations, used to produce many commodity materials, require stabilizing agents to prevent phase separation. Incorporation of these stabilizers in the final polymer may have negative effects on product properties, so the design of new stabilizers is being actively pursued. Amphiphilic diblock copolymers are a promising type of emulsion polymerization stabilizer and are the focus of this work (Fig. 1). First, the tolerance of an amphiphilic diblock copolymer stabilizer’s performance to high molecular weight dispersity and homopolymer impurity has been investigated. Polystyrene-b-poly(acrylic acid) block copolymers were studied due to their previously demonstrated efficacy as stabilizers in emulsion polymerization, and their similarity to commercially important polystyrene-r-poly(acrylic acid) stabilizers. Neither greater molecular weight dispersity nor homopolymer impurity was found to negatively impact the stabilization performance of these block copolymers, suggesting that the economically unfavorable conditions required to achieve low molecular weight dispersity and homopolymer impurity may be avoided. We then examined novel polystyrene-b-[polystyrene-r-poly(acrylic acid)] block-random copolymers which were shown to stabilize emulsion polymerizations with up to 50 weight percent solids content, exceeding what was possible using the polystyrene-b-poly(acrylic acid) block copolymers. Of even greater significance and scientific value is that the block-random copolymers were also observed to have unusual solution behavior, self-folding rather than self-assembling, to give single chain nanoparticles. Emulsion polymerizations stabilized by these block-random copolymers had a total particle surface area which was directly proportional to the stabilizer concentration and was unaffected by polymerization kinetics. A novel “seeded-coagulative” emulsion polymerization mechanism has been proposed to explain these results, which were unexplainable by any known emulsion polymerization mechanism. Please click Additional Files below to see the full abstrac

Phase Separation Driven On-Demand Debondable Waterborne Pressure-Sensitive Adhesives

A waterborne pressure-sensitive adhesive (PSA) that shows high adhesive performance and easy debondability on demand without leaving residues on the substrate (adhesive failure) has been developed. A key component of the PSA is a semicrystalline phase that is beneficial for the adhesive properties and that becomes fluid when heated above the melting temperature. Migration of this liquid-like polymer to the substrate-adhesive interface and hardening upon cooling results in a hard non-tacky interface that facilitates debonding. The effect of the particle morphology on the debonding ability is discussed.This research was funded by AkzoNobe

Fabeln und Fehler

Mit Beiträgen von: Achim Mohné / Uta Kopp, Sabine Rollberg, Michael Erlhoff, CMUK, Hans Ulrich Reck, Laurentia Genske / Robin Humboldt, Dieuwke Boersma, Christian Sievers, Olivier Arciol

Does credit-card information reporting improve small-business tax compliance?

We investigate the response of small businesses operating as sole proprietorships to Form 1099-K, an information report introduced in 2011 which provides the Internal Revenue Service with information about electronic sales (e.g., credit card sales). The overall impact of the policy appears to be relatively small. However, theory and distributional analysis isolates a subset of taxpayers expected to be especially sensitive to reporting, who report receipts equal to or slightly exceeding the receipts reported on 1099-K. Among this set of taxpayers, information reporting induced more complete tax reporting–30% of sensitive taxpayers filed a return declaring business income for the first time, and among those that were already filing, we estimate an increase in reported receipts by up to 24%. These taxpayers largely offset increased reported receipts with increased reported expenses, which do not face information reporting, diminishing the impact on reported net taxable income

Early identification of disease progression in ALK-rearranged lung cancer using circulating tumor DNA analysis

Targeted kinase inhibitors improve the prognosis of lung cancer patients with ALK alterations (ALK+). However, due to the emergence of acquired resistance and varied clinical trajectories, early detection of disease progression is warranted to guide patient management and therapy decisions. We utilized 343 longitudinal plasma DNA samples from 43 ALK+ NSCLC patients receiving ALK-directed therapies to determine molecular progression based on matched panel-based targeted next-generation sequencing (tNGS), and shallow whole-genome sequencing (sWGS). ALK-related alterations were detected in 22 out of 43 (51%) patients. Among 343 longitudinal plasma samples analyzed, 174 (51%) were ctDNA-positive. ALK variant and fusion kinetics generally reflected the disease course. Evidence for early molecular progression was observed in 19 patients (44%). Detection of ctDNA at therapy baseline indicated shorter times to progression compared to cases without mutations at baseline. In patients who succumbed to the disease, ctDNA levels were highly elevated towards the end of life. Our results demonstrate the potential utility of these NGS assays in the clinical management of ALK+ NSCLC

Phase II Trial with Carboplatin and Bendamustine in Patients with Extensive Stage Small-Cell Lung Cancer

Background:Bendamustine is an alkylating agent with hybrid activity and proven efficacy in small-cell lung cancer associated with a favorable toxicity rate. This phase II study of carboplatin/bendamustine was conducted to evaluate the efficacy of this combination in patients with extensive disease small-cell lung cancer (ED-SCLC).Methods:Fifty-six untreated patients with ED-SCLC were enrolled. Their median age was 63 years. Sixty-seven percent of patients were male and 18% had a World Health Organization performance status of 2. Bendamustine was administered as a 30- to 60-minute infusion at a dose of 80 mg/m2 on days 1 and 2, and carboplatin was given at an area under the curve of 5 on day 1 of a 21-day cycle.Results:Fifty-five patients were assessable for response and toxicity. The overall response rate was 72.7% (95% confidence interval: 59%–84%), with one complete remission (1.8%). The median time to progression was 5.2 months (95% confidence interval: 4.2–5.6). At the time of evaluation, 71% of the patients had died. The median survival time reached 8.3 months (95% confidence interval: 6.6–9.9). The major toxicity of this regimen was myelosuppression, including grade 3 or 4 neutropenia (46%), thrombopenia (26%), anemia (15%), and infections (11%). Toxic death was recorded in two patients (3.6%).Conclusions:The carboplatin/bendamustine regimen is a well-tolerated cytostatic combination in ED-SCLC with activity comparable with that of other platinum-based regimens. Further investigations, such as a phase III trial, are currently planned