3,307 research outputs found
Extended electronic states in disordered 1-d lattices: an example
We discuss a very simple model of a 1-d disordered lattice, in which {\em
all} the electronic eigenstates are extended. The nature of these states is
examined from several viewpoints, and it is found that the eigenfunctions are
not Bloch functions although they extend throughout the chain. Some typical
wavefunctions are plotted. This problem originated in our earlier study of
extended states in the quasiperiodic copper-mean lattice [ Sil, Karmakar,
Moitra and Chakrabarti, Phys. Rev. B (1993) ]. In the present investigation
extended states are found to arise from a different kind of correlation than
that of the well-known dimer-type.Comment: 9 pages, 1 figure available on request, LaTex version 2.09,
SINP-SSMP93-0
ICT and environmental sustainability : a case study of a grassroots initiative
Increasingly, local communities develop projects and grassroots
initiatives that address climate change and other environmental sustainability
issues. These projects often commence informally and adopt web-based free
information and communication technologies (ICT) applications to support
their functioning. ICT applications are used to promote the goals of the project,
to recruit more supporters and to facilitate debate among citizens sympathetic to
the cause of environmental stewardship. However, as some of these projects
evolve they become more complex. Struggling with lack of funding, the
solution is to imaginatively combine free web-based ICT applications, to adapt
existing open source applications, and even to develop customized solutions to
address the project’s needs. We present the results of an exploratory case study
of a grassroots initiative with environmental sustainability goals. The study
shows some evidence of innovative practices in the appropriation of ICTs and
in the communication campaign. Implications of this research for online
communities and society are also discussed.Fundação para a Ciência e a Tecnologia (FCT
Dynamic Bayesian Combination of Multiple Imperfect Classifiers
Classifier combination methods need to make best use of the outputs of
multiple, imperfect classifiers to enable higher accuracy classifications. In
many situations, such as when human decisions need to be combined, the base
decisions can vary enormously in reliability. A Bayesian approach to such
uncertain combination allows us to infer the differences in performance between
individuals and to incorporate any available prior knowledge about their
abilities when training data is sparse. In this paper we explore Bayesian
classifier combination, using the computationally efficient framework of
variational Bayesian inference. We apply the approach to real data from a large
citizen science project, Galaxy Zoo Supernovae, and show that our method far
outperforms other established approaches to imperfect decision combination. We
go on to analyse the putative community structure of the decision makers, based
on their inferred decision making strategies, and show that natural groupings
are formed. Finally we present a dynamic Bayesian classifier combination
approach and investigate the changes in base classifier performance over time.Comment: 35 pages, 12 figure
Design of photonic crystal optical waveguides with singlemode propagation in the photonic bandgap
Single-filament Composite MgB2/SUS Ribbons by Powder-In-Tube Process
We report the successful fabrication of single-filament composite MgB2/SUS
ribbons, as an ultra-robust conductor type, employing the powder-in-tube (PIT)
process, by swaging and cold rolling only. The remarkable transport critical
current (Ic) of the non-sintered MgB2/SUS ribbon has observed, as an unexpected
result. Transport critical currents Ic ~ 316 A at T = 4.2 K and Ic ~ 82 A at T
= 20 K were observed at self-field, for the non-sintered composite MgB2/SUS
ribbon. In addition, the persistent current density Jp values, that were
estimated by Bean formula, were more than ~ 7  105 A/cm2 at T = 5 K,
and ~ 1.2  105 A/cm2 at T = 30 K, for the sintered composite MgB2/SUS
ribbon, at H = 0 G.Comment: 10 pages, 4 figure
On the road to carbon reduction in a food supply network: a complex adaptive systems perspective
Purpose: In acknowledging the reality of climate change, large firms have set internal and external (supplier oriented) targets to reduce their greenhouse gas (GHG) emissions. This study explores the complex processes behind the evolution and diffusion of carbon reduction strategies in supply networks.
Design/methodology/approach: The research uses complex adaptive systems (CAS) as a theoretical framework and presents a single case study of a focal buying firm and its supply network in the food sector. A longitudinal and multilevel analysis is used to discuss the dynamics between the focal firm, the supply network and external environment.
Findings: Rather than being a linear and controlled process of adoption-implementation-outcomes, the transition to reduce carbon in a supply network is much more dynamic, emerging as a result of a number of factors at the individual, organizational, supply network and environmental levels.
Research limitations/implications: The research considers the emergence of a carbon reduction strategy in the food sector, driven by a dominant buying firm. Future research should seek to investigate the diffusion of environmental strategies more broadly and in other contexts.
Practical implications: Findings from the research reveal the limits of the control that a buying firm can exert over behaviours in its network and show the positive influence of consortia initiatives on transitioning to sustainability in supply networks.
Originality: CAS is a fairly novel theoretical lens for researching environmental supply network dynamics. The paper offers fresh multilevel insights into the emergent and systemic nature of the diffusion of environmental practices in supply networks
Skyrmions in the Fractional Quantum Hall Effect
It is verified that, at small Zeeman energies, the charged excitations in the
vicinity of 1/3 filled Landau level are skyrmions of composite fermions,
analogous to the skyrmions of electrons near filling factor unity. These are
found to be relevant, however, only at very low magnetic fields.Comment: 13 pages including 2 postscript figures; accepted for publication in
Solid State Communications (1996
Causal mechanisms in the clinical course and treatment of back pain
In recent years, there has been increasing interest in studying causal mechanisms in the development and treatment of back pain. The aim of this article is to provide an overview of our current understanding of causal mechanisms in the field. In the first section, we introduce key concepts and terminology. In the second section, we provide a brief synopsis of systematic reviews of mechanism studies relevant to the clinical course and treatment of back pain. In the third section, we reflect on the findings of our review to explain how understanding causal mechanisms can inform clinical practice and the implementation of best practice. In the final sections, we introduce contemporary methodological advances, highlight the key assumptions of these methods, and discuss future directions to advance the quality of mechanism-related studies in the back pain field
Spin separation in digital ferromagnetic heterostructures
In a study of the ferromagnetic phase of a multilayer digital ferromagnetic
semiconductor in the mean-field and effective-mass approximations, we find the
exchange interaction to have the dominant energy scale of the problem,
effectively controlling the spatial distribution of the carrier spins in the
digital ferromagnetic heterostructures. In the ferromagnetic phase, the
majority and minority carriers tend to be in different regions of the space
(spin separation). Hence, the charge distribution of carriers also changes
noticeably from the ferromagnetic to the paramagnetic phase. An example of a
design to exploit these phenomena is given.Comment: 4 pages, 3 figures. Submitted to Phys. Rev.
Refining the Enrolment Process in Emergency Medicine Research
Research in the emergency setting involving patients with acute clinical conditions is needed if
there are to be advances in diagnosis and treatment. But research in these areas poses ethical and
practical challenges. One of these is the general inability to obtain informed consent due to the
patient’s lack of mental capacity and insufficient time to contact legal representatives. Regulatory
frameworks which allow this research to proceed with a consent ‘waiver’, provided patients lack
mental capacity, miss important ethical subtleties. One of these is the varying nature of mental
capacity among emergency medicine patients. Not only is their capacity variable and often
unclear, but some patients are also likely to be able to engage with the researcher and the context
to varying degrees. In this paper we describe the key elements of a novel enrolment process for
emergency medicine research that refines the consent waiver and fully engages with the ethical
rationale for consent and, in this context, its waiver. The process is verbal but independently
documented during the ‘emergent’ stages of the research. It provides appropriate engagement with
the patient, is context-sensitive and better addresses ethical subtleties. In line with regulation, full
written consent for on-going participation in the research is obtained once the emergency is
passed
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