8,605 research outputs found
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 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
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