970 research outputs found
Magnetic Monopole Dynamics in Spin Ice
One of the most remarkable examples of emergent quasi-particles, is that of
the "fractionalization" of magnetic dipoles in the low energy configurations of
materials known as "spin ice", into free and unconfined magnetic monopoles
interacting via Coulomb's 1/r law [Castelnovo et. al., Nature, 451, 42-45
(2008)]. Recent experiments have shown that a Coulomb gas of magnetic charges
really does exist at low temperature in these materials and this discovery
provides a new perspective on otherwise largely inaccessible phenomenology. In
this paper, after a review of the different spin ice models, we present
detailed results describing the diffusive dynamics of monopole particles
starting both from the dipolar spin ice model and directly from a Coulomb gas
within the grand canonical ensemble. The diffusive quasi-particle dynamics of
real spin ice materials within "quantum tunneling" regime is modeled with
Metropolis dynamics, with the particles constrained to move along an underlying
network of oriented paths, which are classical analogues of the Dirac strings
connecting pairs of Dirac monopoles.Comment: 26 pages, 12 figure
Topological Sector Fluctuations and Curie Law Crossover in Spin Ice
At low temperatures, a spin ice enters a Coulomb phase - a state with
algebraic correlations and topologically constrained spin configurations. In
Ho2Ti2O7, we have observed experimentally that this process is accompanied by a
non-standard temperature evolution of the wave vector dependent magnetic
susceptibility, as measured by neutron scattering. Analytical and numerical
approaches reveal signatures of a crossover between two Curie laws, one
characterizing the high temperature paramagnetic regime, and the other the low
temperature topologically constrained regime, which we call the spin liquid
Curie law. The theory is shown to be in excellent agreement with neutron
scattering experiments. On a more general footing, i) the existence of two
Curie laws appears to be a general property of the emergent gauge field for a
classical spin liquid, and ii) sheds light on the experimental difficulty of
measuring a precise Curie-Weiss temperature in frustrated materials; iii) the
mapping between gauge and spin degrees of freedom means that the susceptibility
at finite wave vector can be used as a local probe of fluctuations among
topological sectors.Comment: 10 pages, 5 figure
Dense colloidal suspensions under time-dependent shear
We consider the nonlinear rheology of dense colloidal suspensions under a
time-dependent simple shear flow. Starting from the Smoluchowski equation for
interacting Brownian particles advected by shearing (ignoring fluctuations in
fluid velocity) we develop a formalism which enables the calculation of
time-dependent, far-from-equilibrium averages. Taking shear-stress as an
example we derive exactly a generalized Green-Kubo relation, and an equation of
motion for the transient density correlator, involving a three-time memory
function. Mode coupling approximations give a closed constitutive equation
yielding the time-dependent stress for arbitrary shear rate history. We solve
this equation numerically for the special case of a hard sphere glass subject
to step-strain.Comment: 4 page
An ethnobotanical survey of medicinal plants used in the East Sepik province of Papua New Guinea
Cues and knowledge structures used by mental-health professionals when making risk assessments
Background: Research into mental-health risks has tended to focus on epidemiological approaches and to consider pieces of evidence in isolation. Less is known about the particular
factors and their patterns of occurrence that influence cliniciansâ risk judgements in practice.
Aims: To identify the cues used by clinicians to make risk judgements and to explore how these combine within cliniciansâ psychological representations of suicide, self-harm, self-neglect, and harm to others.
Method: Content analysis was applied to semi-structured interviews conducted with 46 practitioners from various mental-health disciplines, using mind maps to represent the
hierarchical relationships of data and concepts.
Results: Strong consensus between experts meant their knowledge could be integrated into a single hierarchical structure for each risk. This revealed contrasting emphases between data and concepts underpinning risks, including: reflection and forethought for suicide; motivation
for self-harm; situation and context for harm to others; and current presentation for self-neglect.
Conclusions: Analysis of expertsâ risk-assessment knowledge identified influential cues and their relationships to risks. It can inform development of valid risk-screening decision support systems that combine actuarial evidence with clinical expertise
All-sky interferometric meteor radar meteoroid speed estimation using the Fresnel transform
Fresnel transform meteor speed estimation is investigated. A spectral based technique is developed allowing the transform to be applied at low temporal sampling rates. Simulations are used to compare meteoroid speeds determined using the Fresnel transform and alternative techniques, confirming that the Fresnel transform produces the most accurate meteoroid speed estimates for high effective pulse repetition frequencies (PRFs). The Fresnel transform is applied to high effective PRF data collected during Leonid meteor showers, producing speed estimates in good agreement with the theoretical pre-atmospheric speed of the 71 kmsâ1. Further simulations for the standard low effective PRF sampling parameters used for Buckland Park meteor radar (BPMR) observations suggests that the Fresnel transform can successfully estimate meteor speeds up to 80 kmsâ1. Fresnel transform speed estimation is applied using the BPMR, producing speed distributions similar to those obtained in previous studies. The technique is also applied to data collected using the BPMR sampling parameters during Southern delta-Aquarid and Geminid meteor showers, producing speeds in very good agreement with the theoretical pre-atmospheric speeds of these showers (41 kmsâ1 and 35 kmsâ1, respectively). However, application of the Fresnel transform to high speed showers suggests that the practical upper limit for accurate speed estimation using the BPMR sampling parameters is around 50 kmsâ1. This limit allows speed accurate estimates to be made for about 70% of known meteor showers, and around 70% of sporadic echoes.D. A. Holdsworth, W. G. Elford, R. A. Vincent, I. M. Reid, D. J. Murphy, and W. Singe
Benchmarking food environment policies for the prevention of diet-related non-communicable diseases in Kenya: National expert panelâs assessment and priority recommendations
Introduction: Unhealthy food environments drive the increase of diet-related non-communicable diseases (NCDs).
Objective: We aimed to examine healthy food environment policies in Kenya and identify priorities for future action.
Methods: Using the Healthy Food Environment Policy Index (Food-EPI) we collected evidence on the extent of government action to create healthy food environments across 13 policy and infrastructure support domains and 43 related good practice indicators between 2017 and 2018. A panel of 15 national experts rated the extent of government action on each indicator compared to the policy development cycle and international best practice respectively. Based on gaps found, actions to improve food environments in Kenya were identified and prioritized.
Results: In the policy development cycle, 16/43 (37%) of good practice policy indicators were judged to be in âimplementationâ phase, including: food composition targets, packaged foodsâ ingredient lists/nutrient declarations; systems regulating health claims; restrictions on marketing breast milk substitutes; and school nutrition policies. Infrastructure support actions in âimplementationâ phase included: food-based dietary guidelines; strong political support to reduce NCDs; comprehensive NCD action plan; transparency in developing food policies; and surveys monitoring nutritional status. Half (22/43) of the indicators were judged to be âin developmentâ. Compared to international best practice, the Kenyan Government was judged to be performing relatively well (âmediumâ implementation) in one policy (restrictions on marketing breast milk substitutes) and three infrastructure support areas (political leadership; comprehensive implementation plan; and ensuring all food policies are sensitive to nutrition). Implementation for 36 (83.7 %) indicators were rated as âlowâ or âvery littleâ. Taking into account importance and feasibility, seven actions within the areas of leadership, food composition, labelling, promotion, prices and health-in-all-policies were prioritized.
Conclusion: This baseline assessment is important in creating awareness to address gaps in food environment policy. Regular monitoring using Food-EPI may contribute to addressing the burden of diet-related NCDs in Kenya
Forced mobilization accelerates pathogenesis: characterization of a preclinical surgical model of osteoarthritis
Preclinical osteoarthritis (OA) models are often employed in studies investigating disease-modifying OA drugs (DMOADs). In this study we present a comprehensive, longitudinal evaluation of OA pathogenesis in a rat model of OA, including histologic and biochemical analyses of articular cartilage degradation and assessment of subchondral bone sclerosis. Male Sprague-Dawley rats underwent joint destabilization surgery by anterior cruciate ligament transection and partial medial meniscectomy. The contralateral joint was evaluated as a secondary treatment, and sham surgery was performed in a separate group of animals (controls). Furthermore, the effects of walking on a rotating cylinder (to force mobilization of the joint) on OA pathogenesis were assessed. Destabilization-induced OA was investigated at several time points up to 20 weeks after surgery using Osteoarthritis Research Society International histopathology scores, in vivo micro-computed tomography (CT) volumetric bone mineral density analysis, and biochemical analysis of type II collagen breakdown using the CTX II biomarker. Expression of hypertrophic chondrocyte markers was also assessed in articular cartilage. Cartilage degradation, subchondral changes, and subchondral bone loss were observed as early as 2 weeks after surgery, with considerable correlation to that seen in human OA. We found excellent correlation between histologic changes and micro-CT analysis of underlying bone, which reflected properties of human OA, and identified additional molecular changes that enhance our understanding of OA pathogenesis. Interestingly, forced mobilization exercise accelerated OA progression. Minor OA activity was also observed in the contralateral joint, including proteoglycan loss. Finally, we observed increased chondrocyte hypertrophy during pathogenesis. We conclude that forced mobilization accelerates OA damage in the destabilized joint. This surgical model of OA with forced mobilization is suitable for longitudinal preclinical studies, and it is well adapted for investigation of both early and late stages of OA. The time course of OA progression can be modulated through the use of forced mobilization
Using XML and XSLT for flexible elicitation of mental-health risk knowledge
Current tools for assessing risks associated with mental-health problems require assessors to make high-level judgements based on clinical experience. This paper describes how new technologies can enhance qualitative research methods to identify lower-level cues underlying these judgements, which can be collected by people without a specialist mental-health background.
Methods and evolving results: Content analysis of interviews with 46 multidisciplinary mental-health experts exposed the cues and their interrelationships, which were represented by a mind map using software that stores maps as XML. All 46 mind maps were integrated into a single XML knowledge structure and analysed by a Lisp program to generate quantitative information about the numbers of experts associated with each part of it. The knowledge was refined by the experts, using software developed in Flash to record their collective views within the XML itself. These views specified how the XML should be transformed by XSLT, a technology for rendering XML, which resulted in a validated hierarchical knowledge structure associating patient cues with risks.
Conclusions: Changing knowledge elicitation requirements were accommodated by flexible transformations of XML data using XSLT, which also facilitated generation of multiple data-gathering tools suiting different assessment circumstances and levels of mental-health knowledge
Problematizing Choice: Responsible consumers and sceptical citizens
About the book: Governance, Consumers and Citizens is the first book to bring together a study of governance with consumption, examining the changing place of the consumer as citizen in recent trends in governance, the tensions between competing ideas and practices of consumerism and the active role consumers play in the construction and practice of governance.
Radically pushing forward the debate on consumers and governance, this collection outlines new conceptions and posits new policy agendas. Bringing together international experts from political science, history, geography, social policy and media studies, this study shows how governance and consumption are intertwined in crucial aspects of public policy and contemporary politics
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