Mode I crack tip fields: strain gradient plasticity theory versus J2 flow theory

The mode I crack tip asymptotic response of a solid characterised by strain gradient plasticity is investigated. It is found that elastic strains dominate plastic strains near the crack tip, and thus the Cauchy stress and the strain state are given asymptotically by the elastic K-field. This crack tip elastic zone is embedded within an annular elasto-plastic zone. This feature is predicted by both a crack tip asymptotic analysis and a finite element computation. When small scale yielding applies, three distinct regimes exist: an outer elastic K field, an intermediate elasto-plastic field, and an inner elastic K field. The inner elastic core significantly influences the crack opening profile. Crack tip plasticity is suppressed when the material length scale $\ell$ of the gradient theory is on the order of the plastic zone size estimation, as dictated by the remote stress intensity factor. A generalized J-integral for strain gradient plasticity is stated and used to characterise the asymptotic response ahead of a short crack. Finite element analysis of a cracked three point bend specimen reveals that the crack tip elastic zone persists in the presence of bulk plasticity and an outer J-field

Implementing privacy with Erlang active objects

Functional active objects are a new paradigm for the implementation of services. They offer safe distributed eval- uation with futures and immutable objects guaranteeing efficient implementation of privacy while offering verified quality assurance based on the functional paradigm and a development in an interactive theorem prover. In this paper, we present a novel and highly performant implementation of functional active objects in Erlang. Besides outlining the guiding principles of the interpreter, we show by concrete examples how secure services can be realized

Channeling 5-min photospheric oscillations into the solar outer atmosphere through small-scale vertical magnetic flux tubes

We report two-dimensional MHD simulations which demonstrate that photospheric 5-min oscillations can leak into the chromosphere inside small-scale vertical magnetic flux tubes. The results of our numerical experiments are compatible with those inferred from simultaneous spectropolarimetric observations of the photosphere and chromosphere obtained with the Tenerife Infrared Polarimeter (TIP) at 10830 A. We conclude that the efficiency of energy exchange by radiation in the solar photosphere can lead to a significant reduction of the cut-off frequency and may allow for the propagation of the 5 minutes waves vertically into the chromosphere.Comment: accepted by ApJ

Successful Leadership: Optimizing the Influence of Personality on Work Engagement

Abstract Objective: This paper examines the positive influence that personality has on the level of engagement workers have in their work. By determining the connection between personality characteristics and work engagement, leaders can be proactive in promoting higher levels of engagement by their workers. Background: Engaging in one’s work encompasses the total person and includes elements such as energy, mental resilience, willingness to invest in one’s work, enthusiasm, pride, and the happiness that comes with being involved in work. The level of work engagement of workers in their work has implications for the workers as well as for the organization. Method: Through a review of literature related to personality characteristics and work engagement, the personality characteristics having a positive influence on work engagement are identified. Along with these characteristics, the practical actions associated with these characteristics that have been shown to promote work engagement are discussed. Results: On the basis of literature reviewed, the personality characteristics of conscientiousness, extraversion, and proactive personality were found to have a positive influence on work engagement. Associated with these personality characteristics are a variety of practical actions that impact work engagement. Conclusion: The connection between personality characteristics and engagement in work has been identified. Utilizing practical actions that have been shown to be a positive influence on work engagement is beneficial for the workers as well as for the organization. Application: Leaders can achieve higher levels of success by utilizing the practical actions associated with certain personality characteristics to promote higher levels of work engagement among workers

Pattern formation during diffusion limited transformations in solids

We develop a description of diffusion limited growth in solid-solid transformations, which are strongly influenced by elastic effects. Density differences and structural transformations provoke stresses at interfaces, which affect the phase equilibrium conditions. We formulate equations for the interface kinetics similar to dendritic growth and study the growth of a stable phase from a metastable solid in both a channel geometry and in free space. We perform sharp interface calculations based on Green's function methods and phase field simulations, supplemented by analytical investigations. For pure dilatational transformations we find a single growing finger with symmetry breaking at higher driving forces, whereas for shear transformations the emergence of twin structures can be favorable. We predict the steady state shapes and propagation velocities, which can be higher than in conventional dendritic growth.Comment: submitted to Philosophical Magazin

Züchtungsmethoden in der Diskussion - Brauchen wir Kohl aus Protoplastenfusion?

Bei Kohl aus ökologischem Anbau scheiden sich die Bio-Geister: Kohrabi-, Brokkoli- und Blumenkohlsorten aus Europa und den USA werden zunehmend mit Hilfe umstrittener Züchtungsmethoden wie der gentechnik-nahen Protoplastenfusion angebaut. Werte des Ökolandbaus wie der Erhalt der Artenvielfalt und der Schutz der natürlichen Reproduktionsfähigkeit von Pflanzen werden durch solche Techniken in Frage gestellt. Warum und mit welchem Nutzen sich diese Züchtungsmethode in den letzten Jahren im Gemüseanbau etabliert hat, wird von Fachleuten unterschiedlich beantwortet. Nur mit welchen Konsequenzen? Was sind die Alternativen für Anbau und Handel? Die Protoplastenfusion wird bei Kohl angewendet, um die erbliche Pollensterilität (cytoplasmatic male sterility = CMS) des Rettichs auf verschiedene Kohlarten zu übertragen. Sie erleichtert die Züchtung von Hybriden, die mittlerweile auch im Öko-Landbau weit verbreitet sind - unverdientermaßen, aber das wäre ein weiteres Diskussionsthema..

Canonical Quantization of the Maxwell-Chern-Simons Theory in the Coulomb Gauge

The Maxwell-Chern-Simons theory is canonically quantized in the Coulomb gauge by using the Dirac bracket quantization procedure. The determination of the Coulomb gauge polarization vector turns out to be intrincate. A set of quantum Poincar\'e densities obeying the Dirac-Schwinger algebra, and, therefore, free of anomalies, is constructed. The peculiar analytical structure of the polarization vector is shown to be at the root for the existence of spin of the massive gauge quanta.The Coulomb gauge Feynman rules are used to compute the M\"oller scattering amplitude in the lowest order of perturbation theory. The result coincides with that obtained by using covariant Feynman rules. This proof of equivalence is, afterwards, extended to all orders of perturbation theory. The so called infrared safe photon propagator emerges as an effective propagator which allows for replacing all the terms in the interaction Hamiltonian of the Coulomb gauge by the standard field-current minimal interaction Hamiltonian.Comment: 21 pages, typeset in REVTEX, figures not include

Counterion density profiles at charged flexible membranes

Counterion distributions at charged soft membranes are studied using perturbative analytical and simulation methods in both weak coupling (mean-field or Poisson-Boltzmann) and strong coupling limits. The softer the membrane, the more smeared out the counterion density profile becomes and counterions pentrate through the mean-membrane surface location, in agreement with anomalous scattering results. Membrane-charge repulsion leads to a short-scale roughening of the membrane.Comment: 4 pages, 4 figure