3,781 research outputs found
Band selection and disentanglement using maximally-localized Wannier functions: the cases of Co impurities in bulk copper and the Cu (111) surface
We have adapted the maximally-localized Wannier function approach of [I.
Souza, N. Marzari and D. Vanderbilt, Phys. Rev. B 65, 035109 (2002)] to the
density functional theory based Siesta method [J. M. Soler et al., J. Phys.:
Cond. Mat. 14, 2745 (2002)] and applied it to the study of Co substitutional
impurities in bulk copper as well as to the Cu (111) surface. In the Co
impurity case, we have reduced the problem to the Co d-electrons and the Cu
sp-band, permitting us to obtain an Anderson-like Hamiltonian from well defined
density functional parameters in a fully orthonormal basis set. In order to
test the quality of the Wannier approach to surfaces, we have studied the
electronic structure of the Cu (111) surface by again transforming the density
functional problem into the Wannier representation. An excellent description of
the Shockley surface state is attained, permitting us to be confident in the
application of this method to future studies of magnetic adsorbates in the
presence of an extended surface state
High-Tech Urban Agriculture in Amsterdam : An Actor Network Analysis
The agriculture and horticulture sector in the Netherlands is one of the most productive in the world. Although the sector is one of the most advanced and intense agricultural production systems worldwide, it faces challenges, such as climate change and environmental and social unsustainability of industrial production. To overcome these challenges, alternative food production initiatives have emerged, especially in large cities such as Amsterdam. Some initiatives involve producing food in the urban environment, supported by new technologies and practices, so-called high-tech urban agriculture (HTUA). These initiatives make cultivation of plants inside and on top of buildings possible and increase green spaces in urban areas. The emerging agricultural technologies are creating new business environments that are shape d by technology developers (e.g., suppliers of horticultural light emitting diodes (LED) and control environment systems) and developers of alternative food production practices (e.g., HTUA start-ups). However, research shows that the uptake of these technological innovations in urban planning processes is problematic. Therefore, this research analyzes the barriers that local government planners and HTUA developers are facing in the embedding of HTUA in urban planning processes, using the city of Amsterdam as a case study. This study draws on actor-network theory (ANT) to analyze the interactions between planners, technologies, technology developers and developers of alternative food production practices. Several concepts of ANT are integrated into a multi-level perspective on sustainability transitions (MLP) to create a new theoretical framework that can explain how interactions between technologies and planning actors transform the incumbent social\u2013technical regime. The configuration of interactions between social and material entities in technology development and adoption processes in Amsterdam is analyzed through the lens of this theoretical framework. The data in this study were gathered by tracing actors and their connections by using ethnographic research methods. In the course of the integration of new technologies into urban planning practices, gaps between technologies, technology developers, and planning actors have been identified. The results of this study show a lacking connection between planning actors and technology developers, although planning actors do interact with developers of alternative food production practices. These interactions are influenced by agency of artefacts such as visualizations of the future projects. The paper concludes that for the utilization of emerging technologies for sustainability transition of cities, the existing gap between technology developers and planning actors needs to be bridged through the integration of technology development visions in urban agendas and planning processe
Being While Doing: An Inductive Model of Mindfulness at Work
Mindfulness at work has drawn growing interest as empirical evidence increasingly supports its positive workplace impacts. Yet theory also suggests that mindfulness is a cognitive mode of “Being” that may be incompatible with the cognitive mode of “Doing” that undergirds workplace functioning. Therefore, mindfulness at work has been theorized as “being while doing,” but little is known regarding how people experience these two modes in combination, nor the influences or outcomes of this interaction. Drawing on a sample of 39 semi-structured interviews, this study explores how professionals experience being mindful at work. The relationship between Being and Doing modes demonstrated changing compatibility across individuals and experience, with two basic types of experiences and three types of transitions. We labeled experiences when informants were unable to activate Being mode while engaging Doing mode as Entanglement, and those when informants reported simultaneous co-activation of Being and Doing modes as Disentanglement. This combination was a valuable resource for offsetting important limitations of the typical reliance on the Doing cognitive mode. Overall our results have yielded an inductive model of mindfulness at work, with the core experience, outcomes, and antecedent factors unified into one system that may inform future research and practice.
We did a full hour … of [mindfulness] training… My pager went off like three times. … He\u27s telling us to meditate, and everyone\u27s pager was just beeping. It was not very conducive to meditating. –medical residen
Polymer-Mode-Coupling Theory of Finite-Size-Fluctuation Effects in Entangled Solutions, Melts and Gels. I. General Formulation and Predictions
The transport coefficients of dense polymeric fluids are approximately
calculated from the microscopic intermolecular forces. The following finite
molecular weight effects are discussed within the Polymer-Mode-Coupling theory
(PMC) and compared to the corresponding reptation/ tube ideas: constraint
release mechanism, spatial inhomogeneity of the entanglement constraints, and
tracer polymer shape fluctuations. The entanglement corrections to the single
polymer Rouse dynamics are shown to depend on molecular weight via the ratio
N/N_e, where the entanglement degree of polymerization, N_e, can be measured
from the plateau shear modulus. Two microscopically defined non-universal
parameters, an entanglement strength 1/alpha and a length scale ratio, delta=
xi_rho/b, where xi_rho and b are the density screening and entanglement length
respectively, are shown to determine the reduction of the entanglement effects
relative to the reptation- -like asymptotes of PMC theory. Large finite size
effects are predicted for reduced degrees of polymerization up to N/N_e\le10^3.
Effective power law variations for intermediate N/N_e of the viscosity, eta\sim
N^x, and the diffusion constant, D\sim N^{-y}, can be explained with exponents
significantly exceeding the asymptotic, reptation-like values, x\ge 3 and
y\ge2, respectively. Extensions of the theory to treat tracer dielectric
relaxation, and polymer transport in gels and other amorphous systems, are also
presented.Comment: Latex, figures and styles files included; Macromolecules, in press
(1997
Scalability of GHZ and random-state entanglement in the presence of decoherence
We derive analytical upper bounds for the entanglement of generalized
Greenberger-Horne-Zeilinger states coupled to locally depolarizing and
dephasing environments, and for local thermal baths of arbitrary temperature.
These bounds apply for any convex quantifier of entanglement, and exponential
entanglement decay with the number of constituent particles is found. The
bounds are tight for depolarizing and dephasing channels. We also show that
randomly generated initial states tend to violate these bounds, and that this
discrepancy grows with the number of particles.Comment: 9 pages, 3 figure
On the Dynamics and Disentanglement in Thin and Two-Dimensional Polymer Films
We present results from molecular dynamics simulations of strictly
two-dimensional (2D) polymer melts and thin polymer films in a slit geometry of
thickness of the order of the radius of gyration. We find that the dynamics of
the 2D melt is qualitatively different from that of the films. The 2D monomer
mean-square displacement shows a power law at intermediate times
instead of the law expected from Rouse theory for nonentangled
chains. In films of finite thickness, chain entanglements may occur. The impact
of confinement on the entanglement length has been analyzed by a
primitive path analysis. The analysis reveals that increases
strongly with decreasing film thickness.Comment: 6 pages, 3 figures, proceedings 3rd International Workshop on
Dynamics in Confinement (CONFIT 2006
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