3,688 research outputs found
Understanding the effect resonant magnetic perturbations have on ELMs
All current estimations of the energy released by type I ELMs indicate that,
in order to ensure an adequate lifetime of the divertor targets on ITER, a
mechanism is required to decrease the amount of energy released by an ELM, or
to eliminate ELMs altogether. One such amelioration mechanism relies on
perturbing the magnetic field in the edge plasma region, either leading to more
frequent, smaller ELMs (ELM mitigation) or ELM suppression. This technique of
Resonant Magnetic Perturbations (RMPs) has been employed to suppress type I
ELMs at high collisionality/density on DIII-D, ASDEX Upgrade, KSTAR and JET and
at low collisionality on DIII-D. At ITER-like collisionality the RMPs enhance
the transport of particles or energy and keep the edge pressure gradient below
the 2D linear ideal MHD critical value that would trigger an ELM, whereas at
high collisionality/density the type I ELMs are replaced by small type II ELMs.
Although ELM suppression only occurs within limitied operational ranges, ELM
mitigation is much more easily achieved. The exact parameters that determine
the onset of ELM suppression are unknown but in all cases the magnetic
perturbations produce 3D distortions to the plasma and enhanced particle
transport. The incorporation of these 3D effects in codes will be essential in
order to make quantitative predictions for future devices.Comment: 32 pages, 9 figure
Entrances and exits: changing perceptions of primary teaching as a career for men
Original article can be found at: http://www.informaworld.com/smpp/title~content=t713640830~db=all Copyright Informa / Taylor and Francis. DOI: 10.1080/03004430802352087The number of men in teaching has always been small, particularly in early childhood, but those that do come into teaching usually do so for the same reasons as women, namely enjoyment of working with children, of wanting to teach and wanting to make a difference to children's lives. However, in two separate studies, the authors have shown that on beginning teacher training in 1998, and at the point of leaving the profession in 2005, men and women tend to emphasise different concerns. This article will explore those differences and seek possible explanations for how men's views of teaching might be changing over time.Peer reviewe
Experimental Evidence for Coulomb Charging Effects in an Open Quantum Dot at Zero Magnetic Field
We have measured the low-temperature transport properties of an open quantum
dot formed in a clean one-dimensional channel. For the first time, at zero
magnetic field, continuous and periodic oscillations superimposed upon
ballistic conductance steps are observed when the conductance through the dot
exceeds . We ascribe the observed conductance oscillations to
evidence for Coulomb charging effects in an open dot. This is supported by the
evolution of the oscillating features for as a function of both
temperature and barrier transparency. Our results strongly suggest that at zero
magnetic field, current theoretical and experimental understanding of Coulomb
charging effects overlooks charging in the presence of fully transmitted 1D
channels.Comment: To appear in Phys. Rev. Lett. 81 (Oct 19 issue
Three method factors explaining the low correlations between assessment center dimension ratings and scores on personality inventories
In general, correlations between assessment centre (AC) ratings and personality inventories are low. In this paper, we examine three method factors that may be responsible for these low correlations: differences in (i) rating source (other versus self), (ii) rating domain (general versus specific), and (iii) rating format (multi- versus single item). This study tests whether these three factors diminish correlations between AC exercise ratings and external indicators of similar dimensions. Ratings of personality and performance were combined in an analytical framework following a 2 Ć 2 Ć 2 (source, domain, format) completely crossed, within subjects design. Results showed partial support for the influence of each of the three method factors. Implications for future research are discussed. Copyright Ā© 2004 John Wiley & Sons, Ltd
Internal states of model isotropic granular packings. III. Elastic properties
In this third and final paper of a series, elastic properties of numerically
simulated isotropic packings of spherical beads assembled by different
procedures and subjected to a varying confining pressure P are investigated. In
addition P, which determines the stiffness of contacts by Hertz's law, elastic
moduli are chiefly sensitive to the coordination number, the possible values of
which are not necessarily correlated with the density. Comparisons of numerical
and experimental results for glass beads in the 10kPa-10MPa range reveal
similar differences between dry samples compacted by vibrations and lubricated
packings. The greater stiffness of the latter, in spite of their lower density,
can hence be attributed to a larger coordination number. Voigt and Reuss bounds
bracket bulk modulus B accurately, but simple estimation schemes fail for shear
modulus G, especially in poorly coordinated configurations under low P.
Tenuous, fragile networks respond differently to changes in load direction, as
compared to load intensity. The shear modulus, in poorly coordinated packings,
tends to vary proportionally to the degree of force indeterminacy per unit
volume. The elastic range extends to small strain intervals, in agreement with
experimental observations. The origins of nonelastic response are discussed. We
conclude that elastic moduli provide access to mechanically important
information about coordination numbers, which escape direct measurement
techniques, and indicate further perspectives.Comment: Published in Physical Review E 25 page
Filtering of spin currents based on ballistic ring
Quantum interference effects in rings provide suitable means for controlling
spin at mesoscopic scales. Here we apply such a control mechanism to the
spin-dependent transport in a ballistic quasi one dimensional ring patterned in
two dimensional electron gases (2DEGs). The study is essentially based on the
{\it natural} spin-orbit (SO) interactions, one arising from the laterally
confining electric field {( term) and the other due to to the
quantum-well potential that confines electrons in the 2DEG (conventional Rashba
SO interaction or term).} We focus on single-channel transport and
solve analytically the spin polarization of the current. As an important
consequence of the presence of spin splitting, we find the occurrence of spin
dependent current oscillations.
We analyze %the effects of disorder by discussing the transport in the
presence of one non-magnetic obstacle in the ring. We demonstrate that a spin
polarized current can be induced when an unpolarized charge current is injected
in the ring, by focusing on the central role that the presence of the obstacle
plays.Comment: 9 pages, 7 figures, PACS numbers: 72.25.-b, 72.20.My, 73.50.Jt,
accepted for publication in J. Phys. - Cond. Ma
Generation of folk song melodies using Bayes transforms
The paper introduces the `Bayes transform', a mathematical procedure for putting data into a hierarchical representation. Applicable to any type of data, the procedure yields interesting results when applied to sequences. In this case, the representation obtained implicitly models the repetition hierarchy of the source. There are then natural applications to music. Derivation of Bayes transforms can be the means of determining the repetition hierarchy of note sequences (melodies) in an empirical and domain-general way. The paper investigates application of this approach to Folk Song, examining the results that can be obtained by treating such transforms as generative models
Magnetic-field-induced singularities in spin dependent tunneling through InAs quantum dots
Current steps attributed to resonant tunneling through individual InAs
quantum dots embedded in a GaAs-AlAs-GaAs tunneling device are investigated
experimentally in magnetic fields up to 28 T. The steps evolve into strongly
enhanced current peaks in high fields. This can be understood as a
field-induced Fermi-edge singularity due to the Coulomb interaction between the
tunneling electron on the quantum dot and the partly spin polarized Fermi sea
in the Landau quantized three-dimensional emitter.Comment: 5 pages, 4 figure
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