132 research outputs found
On the importance of parallel magnetic-field fluctuations for electromagnetic instabilities in STEP
No full textThis paper discusses the importance of parallel perturbations of the magnetic-field in gyrokinetic simulations of electromagnetic instabilities and turbulence at mid-radius in the burning plasma phase of the conceptual high-β, reactor-scale, tight-aspect-ratio tokamak STEP. Previous studies have revealed the presence of unstable hybrid kinetic ballooning modes (hKBMs) and subdominant microtearing modes at binormal scales approaching the ion Larmor radius. In this STEP plasma it was found that the hKBM requires the inclusion of parallel magnetic-field perturbations to be linearly unstable. Here, the extent to which the inclusion of fluctuations in the parallel magnetic-field can be relaxed is explored through gyrokinetic simulations. In particular, the frequently used MHD approximation (dropping δB∥ and setting the ∇B drift frequency equal to the curvature drift frequency) is discussed and simulations explore whether this approximation is useful for modelling STEP plasmas. It is shown that the MHD approximation can reproduce some of the linear properties of the full STEP gyrokinetic system, but is too stable at low ky and nonlinear simulations using the MHD approximation result in very different transport states. It is demonstrated that the MHD approximation is challenged by the high β′ values in STEP, and that the approximation improves considerably at lower β′ . Furthermore, it is shown that the sensitivity of STEP to δB∥ fluctuations is primarily because the plasma sits close to marginality and it is shown that in slightly more strongly driven conditions the hKBM is unstable without δB∥. Crucially, it is demonstrated that the state of large transport typically predicted by local electromagnetic gyrokinetic simulations of STEP plasmas is not solely due to δB∥ physics
A quasi-linear model of electromagnetic turbulent transport and its application to flux-driven transport predictions for STEP
No full textA quasi-linear reduced transport model is developed from a database of
high- electromagnetic nonlinear gyrokinetic simulations performed with
Spherical Tokamak for Energy Production (STEP) relevant parameters. The
quasi-linear model is fully electromagnetic and accounts for the effect of
equilibrium flow shear using a novel approach. Its flux predictions are shown
to agree quantitatively with predictions from local nonlinear gyrokinetic
simulations across a broad range of STEP-relevant local equilibria. This
reduced transport model is implemented in the T3D transport solver that is used
to perform the first flux-driven simulations for STEP to account for transport
from hybrid-KBM turbulence, which dominates over a wide region of the core
plasma. Nonlinear gyrokinetic simulations of the final transport steady state
from T3D return turbulent fluxes that are consistent with the reduced model,
indicating that the quasi-linear model may also be appropriate for describing
the transport steady state. Within the assumption considered here, our
simulations support the existence of a transport steady state in STEP with a
fusion power comparable to that in the burning flat-top of the conceptual
design, but do not demonstrate how this state can be accessed
Samoyedic Diary : Early Years of Visual Anthropology in the Soviet Arctic
No full textACKNOWLEDGMENTS The author appreciates the comments and remarks of Craig Campbell (University of Texas, Austin) and of all the participants in the workshop dedicated to the commemoration of Vladimir G. Bogoras, held on May 14, 2015, in the framework of the joint anthropological seminar of the Department of Ethnography of Siberia at the Museum of Anthropology and Ethnography of the Russian Academy of Sciences and the European University at Saint Petersburg. The author also thanks Joselyne Dudding (Museum of Archaeology and Anthropology, University of Cambridge) and David G. Anderson (University of Aberdeen) for a discussion of Ethel John Lindgren's cinematic and photographic materials, which helped in the understanding and contextualization of the Prokofievs’ chronicles. The author is also grateful to Nikolai B. Vakhtin (European University at Saint Petersburg) for his comments on the first version of the article. I am very thankful to Olga Pak for her translation of this article. A Russian version will be published in Antropologicheskii Forum (2016, no. 29). FUNDING This article was written with support from the projects ‘‘Etnos:A life history of theetnosconcept among the Peoplesof the North’’ (European Social Research Council ES=K006428=1) and ‘‘EtnosandMinzu: Histories and Politics ofIdentity Governance in Eurasia’’ (The Leverhulme Trust, IN-2012-138). In addition the Russian Science Foundation(RNF 14-18-02785) supported the archival work in Saint Petersburg during the last stage of the research.Peer reviewe
Repeatability of innervation zone identification in the external anal sphincter muscle
No full textKnowledge of the distribution of the innervation zones (IZs) of the external anal sphincter (EAS) may be useful for preventing anal sphincter incompetence during vaginal delivery. A method proposed for the automatic estimation of the distribution of IZs of EAS from high-density surface electromyography (EMG) was evaluated for repeatability in continent volunteers. Methods: In 13 healthy female subjects (age: 35 11 years) surface EMG signals were acquired using an anal probe with three circumferential electrode arrays (of 16 contacts each) at different depths within the anal canal (15mm distance between the centers of adjacent arrays), during four independent experimental sessions. Three maximal voluntary contractions (MVCs) of 10 sec were performed for each session for a total of 12 contractions per subject. Repeatability of the estimation of the distribution of IZ was tested by evaluating the coefficient of multiple correlations (CMC) between the IZ distributions estimated from the signals recorded from each subject. Results: A high repeatability (CMC > 0.8) was found comparing IZ distributions estimated from signals recorded by each array within the same session. A slightly lower value was obtained considering signals recorded during different sessions (CMC > 0.7), but a higher value (CMC > 0.8) was obtained after aligning the estimated IZ distributions. The realignment compensates for the operator's error in repositioning the probe in the same position during different sessions. Conclusion: This result justifies clinical studies using high-density surface EMG in routine examinations, providing information about IZs of EAS and assessing the possibilities of preventing neuronal trauma during vaginal delivery
Exploring small area demand for grocery retailers in tourist areas
No full textNewing, A., Clarke, G.P. and Clarke, M. 2014. Exploring small area demand for grocery retailers in tourist areas. Tourism Economics, 20(2), pp.407-427This paper uses data from a major loyalty card scheme to draw insights about the characteristics of grocery expenditure by tourists. The authors explore the volume, value and composition of store based visitor expenditure using consumer data from the loyalty card scheme. They focus on grocery spending at selected stores in Cornwall, a popular tourist destination in South West England. Theloyalty card data provide a valuable source rarely available for academic investigations. The authors are able to analyse visitor spend by socio-economic and geodemographic characteristics, drawing a range of comparisons with residential demand from within the store catchment areas. They demonstrate that visitor grocery expenditure is complex and varies by store, destination and type of customer. The paper presents evidence to suggest that the current approaches used to estimate sales uplift and local-level economic impact from visitor demand are unable to account for the complexities of this form of expenditure. Based on these insights, the authors recommend that sophisticated modelling is employed to estimate the impact of visitor expenditure
Comparing pedestal structure in JET-ILW H-mode plasmas with a model for stiff ETG turbulent heat transport
No full textA predictive model for the electron temperature profile of the H-mode pedestal is described, and its results are compared with the pedestal structure of JET-ILW plasmas. The model is based on a scaling for the gyro-Bohm normalized, turbulent electron heat flux qe/qe,gB resulting from electron temperature gradient (ETG) turbulence, derived from results of nonlinear gyrokinetic (GK) calculations for the steep gradient region. By using the local temperature gradient scale length L-Te in the normalization, the dependence of q(e)/q(e,g)B on the normalized gradients R/L-Te and R/(Lne) can be represented by a unified scaling with the parameter eta(e) = L-ne/L-Te, to which the linear stability of ETG turbulence is sensitive when the density gradient is sufficiently steep. For a prescribed density profile, the value of R/L-Te determined from this scaling, required to maintain a constant electron heat flux qe across the pedestal, is used to calculate the temperature profile. Reasonable agreement with measurements is found for different cases, the model providing an explanation of the relative widths and shifts of the T-e and n(e) profiles, as well as highlighting the importance of the separatrix boundary conditions. Other cases showing disagreement indicate conditions where other branches of turbulence might dominate.This article is part of a discussion meeting issue "H-mode transition and pedestal studies in fusion plasmas'
Pedestal particle balance studies in JET-ILW H-mode plasmas
No full textJET-ILW type I ELMy H-modes at 2.5 MA/2.8 T with constant NBI heating (23 MW) and gas fuelling rate were performed, utilising edge localised mode (ELM) pacing by vertical kicks and plasma shaping (triangularity, delta) as tools to disentangle the effects of ELMs, inter-ELM transport and edge stability on the pedestal particle balance. In agreement with previous studies, the pedestal confinement improves with increasing delta, mostly due to a significant increase in pedestal density while the ELM frequency (fELM) is decreased. Improved pedestal confinement with increasing delta was observed even when the pedestal MHD stability was degraded artificially by vertical kicks, implying that increased triangularity may favourably affect the inter-ELM pedestal recovery. The workflow developed to quantify the pedestal particle balance uses high time-resolution profile reflectometry to characterise the inter-ELM evolution of the plasma particle content (dN/dt), the NEO drift-kinetic solver to evaluate the neoclassical fluxes and interpretative EDGE2D-EIRENE simulations to estimate the edge particle source. The edge particle source is then constrained by deuterium Balmer-alpha line intensity measurements in the main chamber, which are, however, strongly affected by reflections from the metal walls. The reflections are accounted for by the CHERAB code taking the divertor emission (the brightest light source in the torus) distribution from imaging spectroscopy measurements as input. Our analysis shows that in the second half of the ELM cycle, the volume-integrated particle source is larger than dN/dt, indicating that transport plays a key role in the inter-ELM pedestal recovery
Recent progress in L-H transition studies at JET: Tritium, Helium, Hydrogen and Deuterium
No full textWe present an overview of results from a series of L-II transition experiments undertaken at JET since the installation of the ITER-like-wall (JET-ILW), with beryllium wall tiles and a tungsten divertor. Tritium, helium and deuterium plasmas have been investigated. Initial results in tritium show ohmic L-H transitions at low density and the power threshold for the L-H transition (P-LH) is lower in tritium plasmas than in deuterium ones at low densities, while we still lack contrasted data to provide a scaling at high densities. In helium plasmas there is a notable shift of the density at which the power threshold is minimum ((n) over bar (e,min)) to higher values relative to deuterium and hydrogen references. Above (n) over bar (e,min) (He) the L-H power threshold at high densities is similar for D and He plasmas. Transport modelling in slab geometry shows that in helium neoclassical transport competes with interchange-driven transport, unlike in hydrogen isotopes. Measurements of the radial electric field in deuterium plasmas show that E-r shear is not a good indicator of proximity to the L-H transition. Transport analysis of ion heat flux in deuterium plasmas show a non-linearity as density is decreased below (n) over bar (e,min). Lastly, a regression of the JET-ILW deuterium data is compared to the 2008 ITPA scaling law
Chronic constipation in adults: Contemporary perspectives and clinical challenges. 2: Conservative, behavioural, medical and surgical treatment
No full textBackground: Chronic constipation is a prevalent disorder that affects quality of life of patients and consumes resources in healthcare systems worldwide. In clinical practice, it is still considered a challenge as clinicians frequently are unsure as to which treatments to use and when. Over a decade ago, a Neurogastroenterology and Motility journal supplement devoted to the investigation and management of constipation was published (Neurogastroenterol Motil 2009;21(Suppl 2):1). In October 2018, the 3rd London Masterclass, entitled “Contemporary management of constipation” was held. The faculty members of this symposium were invited to write two reviews to present a collective synthesis of talks presented and discussions held during this meeting. The first review addresses epidemiology, diagnosis, clinical associations, pathophysiology, and investigation. Purpose: The present is the second of these reviews, providing contemporary perspectives and clinical challenges regarding behavioral, conservative, medical, and surgical treatments for patients presenting with constipation. It includes a management algorithm to guide clinical practice
Testing a prediction model for the H-mode density pedestal against JET-ILW pedestals
No full textThe neutral ionisation model proposed by Groebner et al (2002 Phys. Plasmas 9 2134) to determine the plasma density profile in the H-mode pedestal, is extended to include charge exchange processes in the pedestal stimulated by the ideas of Mahdavi et al (2003 Phys. Plasmas 10 3984). The model is then tested against JET H-mode pedestal data, both in a 'standalone' version using experimental temperature profiles and also by incorporating it in the Europed version of EPED. The model is able to predict the density pedestal over a wide range of conditions with good accuracy. It is also able to predict the experimentally observed isotope effect on the density pedestal that eludes simpler neutral ionization models
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