11,310 research outputs found
Spatiotemporal and Wavenumber Resolved Bicoherence at the Low to High Confinement Transition in the TJ-II Stellarator
Plasma turbulence is studied using Doppler reflectometry at the TJ-II
stellarator. By scanning the tilt angle of the probing beam, different values
of the perpendicular wave numbers are probed at the reflection layer. In this
way, the interaction between zonal flows and turbulence is reported with (a)
spatial, (b) temporal, and (c) wavenumber resolution for the first time in any
magnetic confinement fusion device.
We report measurements of the bicoherence across the Low to High (L--H)
confinement transition at TJ-II. We examine both fast transitions and slow
transitions characterized by an intermediate (I) phase. The bicoherence,
understood to reflect the non-linear coupling between the perpendicular
velocity (zonal flow) and turbulence amplitude, is significantly enhanced in a
time window of several tens of ms around the time of the L--H transition. It is
found to peak at a specific radial position (slightly inward from the radial
electric field shear layer in H mode), and is associated with a specific
perpendicular wave number ( cm, ). In all cases, the bicoherence is due to the interaction between
high frequencies ( MHz) and a rather low frequency (
kHz), as expected for a zonal flow.Comment: 11 pages, 3 figure
Probing the infrared quark mass from highly excited baryons
We argue that three-quark excited states naturally group into quartets, split
into two parity doublets, and that the mass splittings between these parity
partners decrease higher up in the baryon spectrum. This decreasing mass
difference can be used to probe the running quark mass in the mid-infrared
power-law regime. A measurement of masses of high-partial wave Delta*
resonances should be sufficient to unambiguously establish the approximate
degeneracy. We test this concept with the first computation of excited high-j
baryon masses in a chirally invariant quark model.Comment: 4 pages, 4 figures. submitted to Phys Rev Letter
Using highly excited baryons to catch the quark mass
Chiral symmetry in QCD can be simultaneously in Wigner and Goldstone modes,
depending on the part of the spectrum examined. The transition regime between
both, exploiting for example the onset of parity doubling in the high baryon
spectrum, can be used to probe the running quark mass in the mid-IR power-law
regime. In passing we also argue that three-quark states naturally group into
same-flavor quartets, split into two parity doublets, all splittings decreasing
high in the spectrum. We propose that a measurement of masses of high-partial
wave Delta* resonances should be sufficient to unambiguously establish the
approximate degeneracy and see the quark mass running. We test these concepts
with the first computation of the spectrum of high-J excited baryons in a
chiral-invariant quark model.Comment: 6 pages, 9 figures, To appear in the proceedings of the 19th
International IUPAP Conference on Few-Body Problems in Physics; added
acknowledgment, hyphenized author nam
Two-meson cloud contribution to the baryon antidecuplet self-energy
We study the self-energy of the SU(3) antidecuplet coming from two-meson
virtual clouds. Assuming that the exotic Theta+ belongs to an antidecuplet
representation with N(1710) as nucleon partner, we derive effective Lagrangians
that describe the decay of N(1710) into N pi pi with two pions in s- or p-wave.
It is found that the self-energies for all members of the antidecuplet are
attractive, and the larger strangeness particle is more bound. From two-meson
cloud, we obtain about 20 % of the empirical mass splitting between states with
different strangeness.Comment: 4 pages, 2 figures, 1 table, Talk given at the 10th International
Conference on Baryons (Baryons04), Palaiseau (France), October 25-29, 200
Causality detection and turbulence in fusion plasmas
This work explores the potential of an information-theoretical causality
detection method for unraveling the relation between fluctuating variables in
complex nonlinear systems. The method is tested on some simple though nonlinear
models, and guidelines for the choice of analysis parameters are established.
Then, measurements from magnetically confined fusion plasmas are analyzed. The
selected data bear relevance to the all-important spontaneous confinement
transitions often observed in fusion plasmas, fundamental for the design of an
economically attractive fusion reactor. It is shown how the present method is
capable of clarifying the interaction between fluctuating quantities such as
the turbulence amplitude, turbulent flux, and Zonal Flow amplitude, and
uncovers several interactions that were missed by traditional methods.Comment: 26 pages, 14 figure
Macroscopic limit of a kinetic model describing the switch in T cell migration modes via binary interactions
Experimental results on the immune response to cancer indicate that activation of cytotoxic T lymphocytes (CTLs) through interactions with dendritic cells (DCs) can trigger a change in CTL migration patterns. In particular, while CTLs in the pre-activation state move in a non-local search pattern, the search pattern of activated CTLs is more localised. In this paper, we develop a kinetic model for such a switch in CTL migration modes. The model is formulated as a coupled system of balance equations for the one-particle distribution functions of CTLs in the pre-activation state, activated CTLs and DCs. CTL activation is modelled via binary interactions between CTLs in the pre-activation state and DCs. Moreover, cell motion is represented as a velocity-jump process, with the running time of CTLs in the pre-activation state following a long-tailed distribution, which is consistent with a Lévy walk, and the running time of activated CTLs following a Poisson distribution, which corresponds to Brownian motion. We formally show that the macroscopic limit of the model comprises a coupled system of balance equations for the cell densities, whereby activated CTL movement is described via a classical diffusion term, whilst a fractional diffusion term describes the movement of CTLs in the pre-activation state. The modelling approach presented here and its possible generalisations are expected to find applications in the study of the immune response to cancer and in other biological contexts in which switch from non-local to localised migration patterns occurs
Oddballs and a Low Odderon Intercept
We report an odderon Regge trajectory emerging from a field theoretical
Coulomb gauge QCD model for the odd signature JPC (P=C= -1) glueball states
(oddballs). The trajectory intercept is clearly smaller than the pomeron and
even the omega trajectory's intercept which provides an explanation for the
nonobservation of the odderon in high energy scattering data. To further
support this result we compare to glueball lattice data and also perform
calculations with an alternative model based upon an exact Hamiltonian
diagonalization for three constituent gluons.Comment: 4 pages, 2 figures, 1 tabl
- …