122 research outputs found
Nudging or Fudging: The World Development Report 2015
The 2015 World Development Report, Mind Society and Behaviour (World Bank, 2015), seeks a redesign of development policy on the basis of insights emerging from behavioural economics. This paper offers a critical assessment of the Report across four dimensions. First, it situates the Report within the broader and evolving knowledge role of the Bank. Second, the paper locates the Report in the context of the evolution of economics as a discipline and how this informs the evolution of the Bank’s development economics. Third, the Report is critically assessed for its narrow take on behavioural economics itself. Finally, the practical significance of the promotion of behavioural economics is considered through reference to its use in interventions in health in general and in response to HIV/AIDS in particular. It is argued that the Report suggests a dramatic and flawed reduction of what development is about, in that it foregoes any analysis of the structural problems facing developing countries and fails to propose major reforms to tackle these
Magneto-Optical Spectrum Analyzer
We present a method for the investigation of gigahertz magnetization dynamics
of single magnetic nano elements. By combining a frequency domain approach with
a micro focus Kerr effect detection, a high sensitivity to magnetization
dynamics with submicron spatial resolution is achieved. It allows spectra of
single nanostructures to be recorded. Results on the uniform precession in soft
magnetic platelets are presented.Comment: 5 pages, 7 figure
Adaptively time stepping the stochastic Landau-Lifshitz-Gilbert equation at nonzero temperature: implementation and validation in MuMax3
Thermal fluctuations play an increasingly important role in micromagnetic
research relevant for various biomedical and other technological applications.
Until now, it was deemed necessary to use a time stepping algorithm with a
fixed time step in order to perform micromagnetic simulations at nonzero
temperatures. However, Berkov and Gorn have shown that the drift term which
generally appears when solving stochastic differential equations can only
influence the length of the magnetization. This quantity is however fixed in
the case of the stochastic Landau-Lifshitz-Gilbert equation. In this paper, we
exploit this fact to straightforwardly extend existing high order solvers with
an adaptive time stepping algorithm. We implemented the presented methods in
the freely available GPU-accelerated micromagnetic software package MuMax3 and
used it to extensively validate the presented methods. Next to the advantage of
having control over the error tolerance, we report a twenty fold speedup
without a loss of accuracy, when using the presented methods as compared to the
hereto best practice of using Heun's solver with a small fixed time step.Comment: 9 pages, 9 figure
Study of the pitch change of carbon coils during their growth
AbstractIn the present paper, carbon coils (CCs) were prepared by CVD. Their morphology, particularly pitch changes of the carbon coils prepared in different conditions were observed. It was found that the carbon source flow plays an important role in carbon coil growth and its morphology evolution. The appropriate atmosphere and flow rate is beneficial to the steady reactivity of catalyst particles. As such each carbon coil can grow well and have an exact growth rate. When the carbon supply is sufficient, the CCs exhibit close spiral and small coil diameter. When carbon supply decreases, small carbon supply leads to large pitch and coil diameter. CCs can be synthesized with different coil pitch under different carbon supply. This may be of great significance for the controllable preparation of carbon coil and its application
Thermodynamically self-consistent non-stochastic micromagnetic model for the ferromagnetic state
In this work, a self-consistent thermodynamic approach to micromagnetism is
presented. The magnetic degrees of freedom are modeled using the
Landau-Lifshitz-Baryakhtar theory, that separates the different contributions
to the magnetic damping, and thereby allows them to be coupled to the electron
and phonon systems in a self-consistent way. We show that this model can
quantitatively reproduce ultrafast magnetization dynamics in Nickel.Comment: 5 pages, 3 figure
Magnetization structure of a Bloch point singularity
Switching of magnetic vortex cores involves a topological transition
characterized by the presence of a magnetization singularity, a point where the
magnetization vanishes (Bloch point). We analytically derive the shape of the
Bloch point that is an extremum of the free energy with exchange, dipole and
the Landau terms for the determination of the local value of the magnetization
modulus.Comment: 4 pages, 2 figure
Chiral symmetry breaking of magnetic vortices by sample roughness
Finite-element micromagnetic simulations are employed to study the chiral
symmetry breaking of magnetic vortices, caused by the surface roughness of
thin-film magnetic structures. An asymmetry between vortices with different
core polarizations has been experimentally observed for square-shaped
platelets. E.g., the threshold fields for vortex core switching were found to
differ for core up and down. This asymmetry was however not expected for these
symmetrically-shaped structures, where both core polarizations should behave
symmetrically. Three-dimensional finite element simulations are employed to
show that a small surface roughness can break the symmetry between vortex cores
pointing up and down. A relatively small sample roughness is found sufficient
to reproduce the experimentally observed asymmetries. It arises from the lack
of mirror-symmetry of the rough thin-film structures, which causes vortices
with different handedness to exhibit asymmetric dynamics
Is Kapton * Really That Simple?
Age momentum correlation experiments in kapton has revealed the existence of two positron states corresponding to the trapping of positrons on the partially negatively charged O and/or N sites in the polymer chain. A young age broadening of the annihilation line shape is also observed and is attributed to the annihilation in flight of the positrons
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