805 research outputs found
Nanostructure determination from the pair distribution function: A parametric study of the INVERT approach
We present a detailed study of the mechanism by which the INVERT method
[Phys. Rev. Lett. 104, 125501] guides structure refinement of disordered
materials. We present a number of different possible implementations of the
central algorithm and explore the question of algorithm weighting. Our analysis
includes quantification of the relative contributions of variance and
fit-to-data terms during structure refinement, which leads us to study the
roles of density fluctuations and configurational jamming in the RMC fitting
process. We present a parametric study of the pair distribution function
solution space for C60, a-Si and a-SiO2, which serves to highlight the
difficulties faced in developing a transferable weighting scheme.Comment: 15 pages, 7 figures, formatted for JPCM (RMC issue
Plasmonic nanoparticle monomers and dimers: From nano-antennas to chiral metamaterials
We review the basic physics behind light interaction with plasmonic
nanoparticles. The theoretical foundations of light scattering on one metallic
particle (a plasmonic monomer) and two interacting particles (a plasmonic
dimer) are systematically investigated. Expressions for effective particle
susceptibility (polarizability) are derived, and applications of these results
to plasmonic nanoantennas are outlined. In the long-wavelength limit, the
effective macroscopic parameters of an array of plasmonic dimers are
calculated. These parameters are attributable to an effective medium
corresponding to a dilute arrangement of nanoparticles, i.e., a metamaterial
where plasmonic monomers or dimers have the function of "meta-atoms". It is
shown that planar dimers consisting of rod-like particles generally possess
elliptical dichroism and function as atoms for planar chiral metamaterials. The
fabricational simplicity of the proposed rod-dimer geometry can be used in the
design of more cost-effective chiral metamaterials in the optical domain.Comment: submitted to Appl. Phys.
Shape it until you make it: A conceptual foundation for efforts to analyze and shape technological innovation
These are times of accelerating climate change and mass extinction of species on planet Earth. We are in the midst of an ecological crisis that will have profound consequences for human society and its natural environment. While the conditions for life have changed abruptly in the past, the current situation is characterized by the increasing power of a single species. Human beings are not only to blame for the unsustainable practices that brought us here, but also capable of harnessing their combined ingenuity to develop technology that may reduce environmental impacts and provide additional benefits for society. At the same time, the answer to the ecological crisis and other grand challenges is not found in the blind expansion of new technologies. Our success in accomplishing social and environmental objectives rather depends on how, where and when innovation influences patterns of production and consumption. This calls into question the focus of academics and policymakers on stimulating technological innovation. And it highlights the need for analytical tools that can be used to explore how policymakers and other actors may shape the direction of change. The research presented in this thesis therefore aims to develop a conceptual foundation for analyzing and shaping technological innovation. This effort draws on three qualitative case studies that investigate emerging renewable energy technologies from a Swedish perspective. The thesis is situated in the sustainability transitions research community and takes the literature on technological innovation systems as a theoretical point of departure. However, the research adopts a critical perspective and gradually departs from the core concepts used in this literature, over the course of a learning process that unfolds in five appended research papers.In the end, the thesis proposes the technological systems framework as a set of concepts that offers a multidimensional perspective on the dynamics and outcomes of technological innovation. It also presents empirical findings that demonstrate different development trajectories, reveal some of their underlying dynamics and highlight policy implications. This \ua0will hopefully contribute to an ongoing shift in academia and politics – from stimulating the expansion of new technologies, to shaping the direction of change
Deconstructing the glass transition through critical experiments on colloids
The glass transition is the most enduring grand-challenge problem in
contemporary condensed matter physics. Here, we review the contribution of
colloid experiments to our understanding of this problem. First, we briefly
outline the success of colloidal systems in yielding microscopic insights into
a wide range of condensed matter phenomena. In the context of the glass
transition, we demonstrate their utility in revealing the nature of spatial and
temporal dynamical heterogeneity. We then discuss the evidence from colloid
experiments in favor of various theories of glass formation that has
accumulated over the last two decades. In the next section, we expound on the
recent paradigm shift in colloid experiments from an exploratory approach to a
critical one aimed at distinguishing between predictions of competing
frameworks. We demonstrate how this critical approach is aided by the discovery
of novel dynamical crossovers within the range accessible to colloid
experiments. We also highlight the impact of alternate routes to glass
formation such as random pinning, trajectory space phase transitions and
replica coupling on current and future research on the glass transition. We
conclude our review by listing some key open challenges in glass physics such
as the comparison of growing static lengthscales and the preparation of
ultrastable glasses, that can be addressed using colloid experiments.Comment: 137 pages, 45 figure
Glassy dynamics of kinetically constrained models
We review the use of kinetically constrained models (KCMs) for the study of
dynamics in glassy systems. The characteristic feature of KCMs is that they
have trivial, often non-interacting, equilibrium behaviour but interesting slow
dynamics due to restrictions on the allowed transitions between configurations.
The basic question which KCMs ask is therefore how much glassy physics can be
understood without an underlying ``equilibrium glass transition''. After a
brief review of glassy phenomenology, we describe the main model classes, which
include spin-facilitated (Ising) models, constrained lattice gases, models
inspired by cellular structures such as soap froths, models obtained via
mappings from interacting systems without constraints, and finally related
models such as urn, oscillator, tiling and needle models. We then describe the
broad range of techniques that have been applied to KCMs, including exact
solutions, adiabatic approximations, projection and mode-coupling techniques,
diagrammatic approaches and mappings to quantum systems or effective models.
Finally, we give a survey of the known results for the dynamics of KCMs both in
and out of equilibrium, including topics such as relaxation time divergences
and dynamical transitions, nonlinear relaxation, aging and effective
temperatures, cooperativity and dynamical heterogeneities, and finally
non-equilibrium stationary states generated by external driving. We conclude
with a discussion of open questions and possibilities for future work.Comment: 137 pages. Additions to section on dynamical heterogeneities (5.5,
new pages 110 and 112), otherwise minor corrections, additions and reference
updates. Version to be published in Advances in Physic
- …