Publications


The impact of occupancy patterns, occupant-controlled ventilation and shading on indoor overheating risk in domestic environments

BUILDING AND ENVIRONMENT 78 (2014) 183-198

A Mavrogianni, M Davies, J Taylor, Z Chalabi, P Biddulph, E Oikonomou, P Das, B Jones


The relative importance of input weather data for indoor overheating risk assessment in dwellings

BUILDING AND ENVIRONMENT 76 (2014) 81-91

J Taylor, M Davies, A Mavrogianni, Z Chalabi, P Biddulph, E Oikonomou, P Das, B Jones


Effect on plasma rotation of lower hybrid (LH) waves in Alcator C-Mod

AIP Conference Proceedings 1580 (2014) 398-401

JP Lee, M Barnes, RR Parker, JE Rice, FI Parra, PT Bonoli, ML Reinke

The injection of LH waves for current drive into a tokamak changes the ion toroidal rotation. In Alcator C-Mod, the direction of the steady state rotation change due to LH waves depends on the plasma current and the density. The change in rotation can be estimated by balancing the external torque of lower hybrid waves with the turbulent radial transport of the momentum. For high plasma current, the turbulent pinch and diffusion of the injected counter-current momentum are sufficient to explain the rotation change. However, for low plasma current, the change in the the intrinsic momentum transport (residual stress) for a non-rotating state is required to explain the co-current rotation change. Accordingly, we investigate the intrinsic momentum transport for the non-rotating state when diamagnetic flow and ExB flow cancel each other. The change in the intrinsic momentum transport due to lower hybrid waves is significant when the plasma current is low, which may explain the rotation reversal for low plasma current. The effect of changed q (safety factor) profile by lower hybrid on the intrinsic momentum transport is estimated by gyrokinetics. © 2014 AIP Publishing LLC.


Relabeling symmetry in relativistic fluids and plasmas

Journal of Physics A: Mathematical and Theoretical 47 (2014)

Y Kawazura, Z Yoshida, Y Fukumoto

© 2014 IOP Publishing Ltd.The conservation of the recently formulated relativistic canonical helicity (Yoshida et al 2014 J. Math. Phys. 55 043101) is derived from Noether's theorem by constructing an action principle on the relativistic Lagrangian coordinates (we obtain general cross helicities that include the helicity of the canonical vorticity). The conservation law is, then, explained by the relabeling symmetry pertinent to the Lagrangian label of fluid elements. Upon Eulerianizing the Noether current, the purely spatial volume integral on the Lagrangian coordinates is mapped to a space-time mixed three-dimensional integral on the four-dimensional Eulerian coordinates. The relativistic conservation law in the Eulerian coordinates is no longer represented by any divergence-free current; hence, it is not adequate to regard the relativistic helicity (represented by the Eulerian variables) as a Noether charge, and this stands the reason why the 'conventional helicity' is no longer a constant of motion. We have also formulated a relativistic action principle of magnetohydrodynamics (MHD) on the Lagrangian coordinates, and have derived the relativistic MHD cross helicity.


Relativistic helicity and link in Minkowski space-time

Journal of Mathematical Physics 55 (2014)

Z Yoshida, Y Kawazura, T Yokoyama

A relativistic helicity has been formulated in the four-dimensional Minkowski spacetime. Whereas the relativistic distortion of space-time violates the conservation of the conventional helicity, the newly defined relativistic helicity conserves in a barotropic fluid or plasma, dictating a fundamental topological constraint. The relation between the helicity and the vortex-line topology has been delineated by analyzing the linking number of vortex filaments which are singular differential forms representing the pure states of Banach algebra. While the dimension of space-time is four, vortex filaments link, because vorticities are primarily 2-forms and the corresponding 2- chains link in four dimension; the relativistic helicity measures the linking number of vortex filaments that are proper-time cross-sections of the vorticity 2-chains. A thermodynamic force yields an additional term in the vorticity, by which the vortex filaments on a reference-time plane are no longer pure states. However, the vortex filaments on a proper-time plane remain to be pure states, if the thermodynamic force is exact (barotropic), thus, the linking number of vortex filaments conserves. © 2014 AIP Publishing LLC.


A current driven electromagnetic mode in sheared and toroidal configurations (vol 56, 035011, 2014)

PLASMA PHYSICS AND CONTROLLED FUSION 56 (2014) ARTN 129501

I Pusztai, PJ Catto, FI Parra, M Barnes


YOUNG STARS IN AN OLD BULGE: A NATURAL OUTCOME OF INTERNAL EVOLUTION IN THE MILKY WAY

The Astrophysical Journal 787 (2014) L19-L19

M Ness, VP Debattista, T Bensby, S Feltzing, R Roškar, DR Cole, JA Johnson, K Freeman


Erratum: "Correlations at large scales and the onset of turbulence in the fast solar wind" (2013, ApJ, 778, 177)

Astrophysical Journal 782 (2014)

RT Wicks, DA Roberts, A Mallet, AA Schekochihin, TS Horbury, CHK Chen


Bayes versus the virial theorem: inferring the potential of a galaxy from a kinematical snapshot

Monthly Notices of the Royal Astronomical Society 437 (2014) 2230-2248

SJ Magorrian

I present a new framework for estimating a galaxy's gravitational potential, Phi, from its stellar kinematics. It adopts a fully non-parametric model for the galaxy's unknown phase-space distribution function, f, that takes full advantage of Jeans' theorem. Given an expression for the joint likelihood of Phi and f, the likelihood of Phi is calculated by using a Dirichlet process mixture to represent the prior on f and marginalising. I demonstrate that modelling machinery constructed using this framework is successful at recovering the potentials of some simple systems given perfect kinematical data, a situation handled effortlessly by traditional moment-based methods, such as the virial theorem, but in which the more modern extended-Schwarzschild method fails. Unlike moment-based methods, however, the models constructed using this framework can easily be generalised to take account of realistic observational errors and selection functions.


Interstellar medium. Pseudo-three-dimensional maps of the diffuse interstellar band at 862 nm.

Science (New York, N.Y.) 345 (2014) 791-795

J Kos, T Zwitter, R Wyse, O Bienaymé, J Binney, J Bland-Hawthorn, K Freeman, BK Gibson, G Gilmore, EK Grebel, A Helmi, G Kordopatis, U Munari, J Navarro, Q Parker, WA Reid, G Seabroke, S Sharma, A Siebert, A Siviero, M Steinmetz, FG Watson, ME Williams

The diffuse interstellar bands (DIBs) are absorption lines observed in visual and near-infrared spectra of stars. Understanding their origin in the interstellar medium is one of the oldest problems in astronomical spectroscopy, as DIBs have been known since 1922. In a completely new approach to understanding DIBs, we combined information from nearly 500,000 stellar spectra obtained by the massive spectroscopic survey RAVE (Radial Velocity Experiment) to produce the first pseudo-three-dimensional map of the strength of the DIB at 8620 angstroms covering the nearest 3 kiloparsecs from the Sun, and show that it follows our independently constructed spatial distribution of extinction by interstellar dust along the Galactic plane. Despite having a similar distribution in the Galactic plane, the DIB 8620 carrier has a significantly larger vertical scale height than the dust. Even if one DIB may not represent the general DIB population, our observations outline the future direction of DIB research.


Equivalence of two independent calculations of the higher order guiding center Lagrangian

PHYSICS OF PLASMAS 21 (2014) ARTN 104506

FI Parra, I Calvo, JW Burby, J Squire, H Qin


KINEMATIC MODELING OF THE MILKY WAY USING THE RAVE AND GCS STELLAR SURVEYS

ASTROPHYSICAL JOURNAL 793 (2014) ARTN 51

S Sharma, J Bland-Hawthorn, J Binney, KC Freeman, M Steinmetz, C Boeche, O Bienayme, BK Gibson, GF Gilmore, EK Grebel, A Helmi, G Kordopatis, U Munari, JF Navarro, QA Parker, WA Reid, GM Seabroke, A Siebert, F Watson, MEK Williams, RFG Wyse, T Zwitter


Why stellar feedback promotes disc formation in simulated galaxies

Monthly Notices of the Royal Astronomical Society 443 (2014) 2092-2111

H Übler, T Naab, L Oser, M Aumer, LV Sales, SDM White

We study how feedback influences baryon infall on to galaxies using cosmological, zoom-in simulations of haloes with present mass Mvir = 6.9 × 1011 to 1.7 × 1012M⊙. Starting at z = 4 from identical initial conditions, implementations of weak and strong stellar feedback produce bulge- and disc-dominated galaxies, respectively. Strong feedback favours disc formation: (1) because conversion of gas into stars is suppressed at early times, as required by abundance matching arguments, resulting in flat star formation histories and higher gas fractions; (2) because 50 per cent of the stars form in situ from recycled disc gas with angular momentum only weakly related to that of the z = 0 dark halo; (3) because late-time gas accretion is typically an order of magnitude stronger and has higher specific angular momentum, with recycled gas dominating over primordial infall; (4) because 25-30 per cent of the total accreted gas is ejected entirely before z ̃ 1, removing primarily low angular momentum material which enriches the nearby intergalactic medium. Most recycled gas roughly conserves its angular momentum, but material ejected for long times and to large radii can gain significant angular momentum before re-accretion. These processes lower galaxy formation efficiency in addition to promoting disc formation. © 2014 The Authors.Published by Oxford University Press on behalf of the Royal Astronomical Society.


Suppression of local heat flux in a turbulent magnetized intracluster medium

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 440 (2014) 1153-1164

SV Komarov, EM Churazov, AA Schekochihin, JA ZuHone


The Gaia-ESO Survey: The analysis of high-resolution UVES spectra of FGK-type stars

ASTRONOMY & ASTROPHYSICS 570 (2014) ARTN A122

R Smiljanic, AJ Korn, M Bergemann, A Frasca, L Magrini, T Masseron, E Pancino, G Ruchti, I San Roman, L Sbordone, SG Sousa, H Tabernero, G Tautvaisiene, M Valentini, M Weber, CC Worley, VZ Adibekyan, C Allende Prieto, G Barisevicius, K Biazzo, S Blanco-Cuaresma, P Bonifacio, A Bragaglia, E Caffau, T Cantat-Gaudin, Y Chorniy, P de Laverny, E Delgado-Mena, P Donati, S Duffau, E Franciosini, E Friel, D Geisler, JI Gonzalez Hernandez, P Gruyters, G Guiglion, CJ Hansen, U Heiter, V Hill, HR Jacobson, P Jofre, H Jonsson, AC Lanzafame, C Lardo, H-G Ludwig, E Maiorca, S Mikolaitis, D Montes, T Morel, A Mucciarelli, C Munoz, T Nordlander, L Pasquini, E Puzeras, A Recio-Blanco, N Ryde, G Sacco, NC Santos, AM Serenelli, R Sordo, C Soubiran, L Spina, M Steffen, A Vallenari, S Van Eck, S Villanova, G Gilmore, S Randich, M Asplund, J Binney, J Drew, S Feltzing, A Ferguson, R Jeffries, G Micela, I Negueruela, T Prusti, H-W Rix, E Alfaro, C Babusiaux, T Bensby, R Blomme, E Flaccomio, P Francois, M Irwin, S Koposov, N Walton, A Bayo, G Carraro, MT Costado, F Damiani, B Edvardsson, A Hourihane, R Jackson, J Lewis, K Lind, G Marconi, C Martayan, L Monaco, L Morbidelli, L Prisinzano, S Zaggia


Inboard and outboard radial electric field wells in the H- and I-mode pedestal of Alcator C-Mod and poloidal variations of impurity temperature

NUCLEAR FUSION 54 (2014) ARTN 083017

C Theiler, RM Churchill, B Lipschultz, M Landreman, DR Ernst, JW Hughes, PJ Catto, FI Parra, IH Hutchinson, ML Reinke, AE Hubbard, ES Marmar, JT Terry, JR Walk, AC-M Team


Reduction of core turbulence in I-mode plasmas in Alcator C-Mod

NUCLEAR FUSION 54 (2014) ARTN 083019

AE White, M Barnes, A Dominguez, M Greenwald, NT Howard, AE Hubbard, JW Hughes, DR Mikkelsen, FI Parra, ML Reinke, C Sung, J Walk, DG Whyte


The final-parsec problem in nonspherical galaxies revisited

Astrophysical Journal 785 (2014)

E Vasiliev, F Antonini, D Merritt

We consider the evolution of supermassive black hole binaries at the center of spherical, axisymmetric, and triaxial galaxies, using direct N-body integrations as well as analytic estimates. We find that the rates of binary hardening exhibit a significant N-dependence in all the models, at least for N in the investigated range of 105 ≤ N ≤ 106. Binary hardening rates are also substantially lower than would be expected if the binary "loss cone" remained "full," as it would be if the orbits supplying stars to the binary were being efficiently replenished. The difference in binary hardening rates between the spherical and nonspherical models is less than a factor of two even in the simulations with the largest N. By studying the orbital populations of our models, we conclude that the rate of supply of stars to the binary via draining of centrophilic orbits is indeed expected to be much lower than the full-loss-cone rate, consistent with our simulations. We argue that the binary's evolution in the simulations is driven in roughly equal amounts by collisional and collisionless effects, even at the highest N-values currently accessible. While binary hardening rates would probably reach a limiting value for large N, our results suggest that we cannot approach that rate with currently available algorithms and computing hardware. The extrapolation of results from N-body simulations to real galaxies is therefore not straightforward, casting doubt on recent claims that triaxiality or axisymmetry alone are capable of solving the final-parsec problem in gas-free galaxies. © 2014. The American Astronomical Society. All rights reserved.


LINE-DRIVEN DISK WINDS IN ACTIVE GALACTIC NUCLEI: THE CRITICAL IMPORTANCE OF IONIZATION AND RADIATIVE TRANSFER

The Astrophysical Journal 789 (2014) 19-19

N Higginbottom, D Proga, C Knigge, KS Long, JH Matthews, SA Sim


Comparison of BES measurements of ion-scale turbulence with direct gyro-kinetic simulations of MAST L-mode plasmas

Plasma Physics and Controlled Fusion 56 (2014)

AR Field, D Dunai, YC Ghim, P Hill, B McMillan, CM Roach, S Saarelma, AA Schekochihin, S Zoletnik

Observations of ion-scale (kyρi 1) density turbulence of relative amplitude 0.2% are available on the Mega Amp Spherical Tokamak (MAST) using a 2D (8 radial × 4 poloidal channel) imaging beam emission spectroscopy diagnostic. Spatial and temporal characteristics of this turbulence, i.e., amplitudes, correlation times, radial and perpendicular correlation lengths and apparent phase velocities of the density contours, are determined by means of correlation analysis. For a low-density, L-mode discharge with strong equilibrium flow shear exhibiting an internal transport barrier in the ion channel, the observed turbulence characteristics are compared with synthetic density turbulence data generated from global, non-linear, gyro-kinetic simulations using the particle-in-cell code NEMORB. This validation exercise highlights the need to include increasingly sophisticated physics, e.g., kinetic treatment of trapped electrons, equilibrium flow shear and collisions, to reproduce most of the characteristics of the observed turbulence. Even so, significant discrepancies remain: an underprediction by the simulations of the turbulence amplitude and heat flux at plasma periphery and the finding that the correlation times of the numerically simulated turbulence are typically two orders of magnitude longer than those measured in MAST. Comparison of these correlation times with various linear timescales suggests that, while the measured turbulence is strong and may be 'critically balanced', the simulated turbulence is weak. © 2014 IOP Publishing Ltd.

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