3,089 research outputs found
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Diagnostics for magnetically confined high-temperature plasmas
During the last 20 years, magnetically confined laboratory plasmas of steadily increasing temperatures and densities have been obtained, most notably in tokamak configurations, and now approach the conditions necessary to sustain a fusion reaction. Even more important to the goal of understanding the physics of such systems, remarkable advances in plasma diagnostics, the techniques for determining the properties of such plasmas, have accompanied these developments. More parameters can be determined with greater accuracy and finer spatial and temporal resolution. The magnetic configuration, the primary local thermodynamic quantities (density, temperature, and drift velocity), and other necessary quantities can now be measured with sufficient accuracy to determine particle and energy fluxes within the plasma and to characterize the basic transport processes. These plasmas are far from thermodynamic equilibrium. This deviation manifests itself in a variety of instabilities on several spatial and temporal scales, many of which are aptly described as turbulence. Many aspects of the turbulence can also be characterized. This article reviews the current state of diagnostics from an epistemoiogical perspective: the capabilities and limitations for measuring each important physical quantity are presented.Physic
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A parsimonious model for the proportional control valve
A generic non-linear dynamic model of a direct-acting electrohydraulic proportional solenoid valve is presented. The valve consists of two subsystems-s-a spool assembly and one or two unidirectional proportional solenoids. These two subsystems are modelled separately. The solenoid is modelled as a non-linear resistor-inductor combination, with inductance parameters that change with current. An innovative modelling method has been used to represent these components. The spool assembly is modelled as a mass-spring-damper system. The inertia and the damping effects of the solenoid armature are incorporated in the spool mode1. The model accurately and reliably predicts both the dynamic and steady state responses of the valve to voltage inputs. Simulated results are presented, which agree well with experimental results
Entanglement entropy of Wilson loops: Holography and matrix models
A half-BPS circular Wilson loop in supersymmetric
Yang-Mills theory in an arbitrary representation is described by a Gaussian
matrix model with a particular insertion. The additional entanglement entropy
of a spherical region in the presence of such a loop was recently computed by
Lewkowycz and Maldacena using exact matrix model results. In this note we
utilize the supergravity solutions that are dual to such Wilson loops in a
representation with order boxes to calculate this entropy
holographically. Employing the matrix model results of Gomis, Matsuura, Okuda
and Trancanelli we express this holographic entanglement entropy in a form that
can be compared with the calculation of Lewkowycz and Maldacena. We find
complete agreement between the matrix model and holographic calculations.Comment: 17 pages, 1 figur
Lifshitz entanglement entropy from holographic cMERA
We study entanglement entropy in free Lifshitz scalar field theories
holographically by employing the metrics proposed by Nozaki, Ryu and Takayanagi
in \cite{Nozaki:2012zj} obtained from a continuous multi-scale entanglement
renormalisation ansatz (cMERA). In these geometries we compute the minimal
surface areas governing the entanglement entropy as functions of the dynamical
exponent and we exhibit a transition from an area law to a volume law
analytically in the limit of large . We move on to explore the effects of a
massive deformation, obtaining results for any in arbitrary dimension. We
then trigger a renormalisation group flow between a Lifshitz theory and a
conformal theory and observe a monotonic decrease in entanglement entropy along
this flow. We focus on strip regions but also consider a disc in the undeformed
theory.Comment: 17 pages, v2: references added and improved discussions, v3:
published versio
On the convergence of Regge calculus to general relativity
Motivated by a recent study casting doubt on the correspondence between Regge
calculus and general relativity in the continuum limit, we explore a mechanism
by which the simplicial solutions can converge whilst the residual of the Regge
equations evaluated on the continuum solutions does not. By directly
constructing simplicial solutions for the Kasner cosmology we show that the
oscillatory behaviour of the discrepancy between the Einstein and Regge
solutions reconciles the apparent conflict between the results of Brewin and
those of previous studies. We conclude that solutions of Regge calculus are, in
general, expected to be second order accurate approximations to the
corresponding continuum solutions.Comment: Updated to match published version. Details of numerical calculations
added, several sections rewritten. 9 pages, 4 EPS figure
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Finite element modelling and load share analysis for involute worm gears with localised tooth contact
A new approach has been developed by the authors to estimate the load share of worm gear drives, and to calculate the instantaneous tooth meshing stiffness and loaded transmission errors. In the approach, the finite element (FE) modelling is based on the modified tooth geometry, which ensures that the worm gear teeth are in localized contact. The geometric modelling method for involute worm gears allows the tooth elastic deformation and tooth root stresses of worm gear drives under different load conditions to be investigated. On the basis of finite element analysis, the instantaneous meshing stiffness and loaded transmission errors are obtained and the load share is predicted. In comparison with existing methods, this approach applies loaded tooth contact analysis and provides more accurate load capacity rating of worm gear drives
A brief review of Regge calculus in classical numerical relativity
We briefly review past applications of Regge calculus in classical numerical
relativity, and then outline a programme for the future development of the
field. We briefly describe the success of lattice gravity in constructing
initial data for the head-on collision of equal mass black holes, and discuss
recent results on the efficacy of Regge calculus in the continuum limit.Comment: 2 pages, submitted to the Proceedings of the IX Marcel Grossmann
Meeting, Rome, July 2-8, 200
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