174 research outputs found
ECCD-induced sawtooth crashes at W7-X
The optimised superconducting stellarator W7-X generates its rotational transform by means of
external coils, therefore no toroidal current is necessary for plasma confinement. Electron
cyclotron current drive experiments were conducted for strikeline control and safe divertor
operation. During current drive experiments periodic and repetitive crashes of the central
electron temperature, similar to sawtooth crashes in tokamaks, were detected. Measurements
from soft x-ray tomography and electron cyclotron emission show that the crashes are preceded
by weak oscillating precursors and a displacement of the plasma core, consistent with a
(m, n)=(1, 1) mode. The displacement occurs within 100μs, followed by expulsion and
redistribution of the core into the external part of the plasma. Two types of crashes, with
different frequencies and amplitudes are detected in the experimental program. For these
non-stationary parameters a strong dependence on the toroidal current is found. A 1-D heuristic
model for current diffusion is proposed as a first step to explain the characteristic crash time.
Initial results show that the modelled current diffusion timescale is consistent with the initial
crash frequency and that the toroidal current rise shifts the position where the instability is
triggered, resulting in larger crash amplitudes
Factors influencing patient satisfaction with dental appearance and treatments they desire to improve aesthetics
Background: We assessed factors influencing patients’ satisfaction with their dental appearance and the
treatments they desired to improve dental aesthetics.
Methods: A cross-sectional study was performed out among 235 adult patients who visited the Hospital Universiti
Sains Malaysia dental clinic. A structured, interviewer-guided questionnaire was used to identify patient satisfaction
with their general dental appearance, cosmetic elements and desired treatments.
Results: The 235 patients consisted of 70 males (29.8%) and 165 females (70.2%), of mean age 31.5 years (SD 13.0).
Of these patients, 124 (52.8%) were not satisfied with their general dental appearance. In addition, 132 patients
(56.2%) were not happy with the color of their teeth, 76 (32.3%), regarded their teeth were poorly aligned, 62
(26.4%), as crowded and 56 (23.4%) protruded. Dissatisfaction with tooth color was significantly higher in female
than in male patients (odds ratio [OR] of 1.99 (95% confidence interval [CI] 1.13-3.50). Tooth whitening was the
treatment most desired by patients (48.1%). Results of multiple logistic regression analysis showed that patient
dissatisfaction with general dental appearance was significantly associated with female gender (OR = 2.18; 95% CI:
1.18-4.03), unhappiness with tooth color (OR = 3.05; 95% CI: 1.74-5.34) and the opinion that their teeth protruded
(OR = 2.91, 95% CI: 1.44-5.91)
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