972 research outputs found
Analyzing epsilon'/epsilon in the 1/N_c Expansion
We present a recent analysis of epsilon'/epsilon in the 1/N_c expansion. We
show that the 1/N_c corrections to the matrix element of Q_6 are large and
positive, indicating a Delta I=1/2 enhancement similar to the one of Q_1 and
Q_2 which dominate the CP conserving amplitude. This enhances the CP ratio and
can bring the standard model prediction close to the measured value for central
values of the parameters.Comment: One reference corrected. 5 pages, talk presented by P.H. Soldan at
the 3. International Conference on B Physics and CP Violation, Taipei,
Taiwan, December 3 - 7, 1999. Slightly expanded version of the article
submitted to the proceeding
Interpretation of runaway electron synchrotron and bremsstrahlung images
The crescent spot shape observed in DIII-D runaway electron synchrotron
radiation images is shown to result from the high degree of anisotropy in the
emitted radiation, the finite spectral range of the camera and the distribution
of runaways. The finite spectral camera range is found to be particularly
important, as the radiation from the high-field side can be stronger by a
factor than the radiation from the low-field side in DIII-D. By
combining a kinetic model of the runaway dynamics with a synthetic synchrotron
diagnostic we see that physical processes not described by the kinetic model
(such as radial transport) are likely to be limiting the energy of the
runaways. We show that a population of runaways with lower dominant energies
and larger pitch-angles than those predicted by the kinetic model provide a
better match to the synchrotron measurements. Using a new synthetic
bremsstrahlung diagnostic we also simulate the view of the Gamma Ray Imager
(GRI) diagnostic used at DIII-D to resolve the spatial distribution of
runaway-generated bremsstrahlung.Comment: 21 pages, 11 figure
Recommended from our members
Priming of Familiar and Unfamiliar Visual Objects over Delays in Young and Older Adults
Although priming of familiar stimuli is usually age invariant, little is known about how aging affects priming of preexperimentally unfamiliar stimuli. Therefore, this study investigated the effects of aging and encoding-to-test delays (0 min, 20 min, 90 min, and 1 week) on priming of unfamiliar objects in block-based priming paradigms. During the encoding phase, participants viewed pictures of novel objects (Experiments 1 and 2) or novel and familiar objects (Experiment 3) and judged their left-right orientation. In the test block, priming was measured using the possible-impossible object-decision test (Experiment 1), symmetric-asymmetric object-decision test (Experiment 2), and real-nonreal object-decision test (Experiment 3). In Experiments 1 and 2, young adults showed priming for unfamiliar objects at all delays, whereas older adults whose baseline task performance was similar to that of young adults did not show any priming. Experiment 3 found no effects of age or delay on priming of familiar objects; however, priming of unfamiliar objects was only observed in the young participants. This suggests that when older adults cannot rely on preexisting memory representations, age-related deficits in priming can emerge
Experimental conditions to suppress edge localised modes by magnetic perturbations in the ASDEX Upgrade tokamak
Access conditions for full suppression of Edge Localised Modes (ELMs) by
Magnetic Perturbations (MP) in low density high confinement mode (H-mode)
plasmas are studied in the ASDEX Upgrade tokamak. The main empirical
requirements for full ELM suppression in our experiments are: 1. The poloidal
spectrum of the MP must be aligned for best plasma response from weakly stable
kink-modes, which amplify the perturbation, 2. The plasma edge density must be
below a critical value, ~m. The edge collisionality
is in the range (ions) and
(electrons). However, our data does not show that the edge collisionality is
the critical parameter that governs access to ELM suppression. 3. The pedestal
pressure must be kept sufficiently low to avoid destabilisation of small ELMs.
This requirement implies a systematic reduction of pedestal pressure of
typically 30\% compared to unmitigated ELMy H-mode in otherwise similar
plasmas. 4. The edge safety factor lies within a certain window.
Within the range probed so far, , one such window,
has been identified. Within the range of plasma rotation
encountered so far, no apparent threshold of plasma rotation for ELM
suppression is found. This includes cases with large cross field electron flow
in the entire pedestal region, for which two-fluid MHD models predict that the
resistive plasma response to the applied MP is shielded
Assessment of vertical stability for negative triangularity pilot plants
Negative triangularity (NT) tokamak configurations may be more susceptible to
magneto-hydrodynamic instability, posing challenges for recent reactor designs
centered around their favorable properties, such as improved confinement and
operation free of edge-localized modes. In this work, we assess the vertical
stability of plasmas with NT shaping and develop potential reactor solutions.
When coupled with a conformal wall, NT equilibria are confirmed to be less
vertically stable than equivalent positive triangularity (PT) configurations.
Unlike PT, their vertical stability is degraded at higher poloidal beta.
Furthermore, improvements in vertical stability at low aspect ratio do not
translate to the NT geometry. NT equilibria are stabilized in PT vacuum vessels
due to the increased proximity of the plasma and the wall on the outboard side,
but this scenario is found to be undesirable due to reduced vertical gaps which
give less spatial margin for control recovery. Instead, we demonstrate that
informed positioning of passively conducting plates can lead to improved
vertical stability in NT configurations on par with stability metrics expected
in PT scenarios. An optimal setup for passive plates in highly elongated NT
devices is presented, where plates on the outboard side of the device reduce
vertical instability growth rates to 16% of their baseline value. For lower
target elongations, integration of passive stabilizers with divertor concepts
can lead to significant improvements in vertical stability. Plates on the
inboard side of the device are also uniquely enabled in NT geometries,
providing opportunity for spatial separation of vertical stability coils and
passive stabilizers
C. trachomatis pgp3 antibody prevalence in young women in England, 1993-2010
Seroepidemiology of chlamydia can offer study opportunities and insights into cumulative risk of exposure that may contribute to monitoring the frequency of, and control of, genital chlamydia-the most commonly diagnosed STI in England. We undertook retrospective anonymous population-based cross-sectional surveys using an indirect IgG ELISA for chlamydia Pgp3 antibody. Sera from 4,732 women aged 17-24 years were tested. Samples were taken at 3-yearly intervals between 1993 and 2002, a period during which other data suggest chlamydia transmission may have been increasing, and from each year between 2007 and 2010. Seroprevalence increased in 17-24 year olds over time between 1993 and 2002. Between 2007 and 2010, age-standardised seroprevalence among 17-24 year olds decreased from 20% (95% CI: 17-23) to 15% (95%CI 12-17) (p = 0.0001). The biggest drop was among 20 to 21 year olds, where seroprevalence decreased from 21% in 2007 to 9% in 2010 (p = 0.002). These seroprevalence data reflect some known features of the epidemiology of chlamydia infection, and show that exposure to antibody-inducing chlamydia infection has declined in recent years. This decline was concurrent with increasing rates of screening for asymptomatic chlamydia. Serology should be explored further as a tool for evaluation of chlamydia control, including chlamydia screening programmes
Observation of a multimode plasma response and its relationship to density pumpout and edge-localized mode suppression
Density pumpout and edge-localized mode (ELM) suppression by applied n=2 magnetic fields in low-collisionality DIII-D plasmas are shown to be correlated with the magnitude of the plasma response driven on the high-field side (HFS) of the magnetic axis but not the low-field side (LFS) midplane. These distinct responses are a direct measurement of a multimodal magnetic plasma response, with each structure preferentially excited by a different n=2 applied spectrum and preferentially detected on the LFS or HFS. Ideal and resistive magneto-hydrodynamic (MHD) calculations find that the LFS measurement is primarily sensitive to the excitation of stable kink modes, while the HFS measurement is primarily sensitive to resonant currents (whether fully shielding or partially penetrated). The resonant currents are themselves strongly modified by kink excitation, with the optimal applied field pitch for pumpout and ELM suppression significantly differing from equilibrium field alignment.This material is based upon work supported by the U.S.
Department of Energy, Office of Science, Office of Fusion
Energy Sciences, using the DIII-D National Fusion Facility,
a DOE Office of Science user facility, under Awards No. DE-FC02-04ER54698, No. DE-AC02-09CH11466,
No. DE-FG02-04ER54761, No. DE-AC05-06OR23100,
No. DE-SC0001961, and No. DE-AC05-00OR22725.
S. R. H. was supported by AINSE and ANSTO
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