1,057 research outputs found
Dynamics of plasma blobs in a shear flow
The global dynamic of plasma blobs in a shear flow is investigated in a simple magnetized torus using
the spatial Fourier harmonics (k-space) framework. Direct experimental evidence of a linear drift in
k space of the density fluctuation energy synchronized with blob events is presented. During this drift, an
increase of the fluctuation energy and a production of the kinetic energy associated with blobs are observed.
The energy source of the blob is analyzed using an advection-dissipation-type equation that includes
blob-flow exchange energy, linear drift in k space, nonlinear processes, and viscous dissipations.
We show that blobs tap their energy from the dominant E B vertical background flow during the linear
drift stage. The exchange of energy is unidirectional as there is no evidence that blobs return energy to the
flow
Time-energy correlations in solar flare occurrence
The existence of time-energy correlations in flare occurrence is still an
open and much debated problem. This study addresses the question whether
statistically significant correlations are present between energies of
successive flares as well as energies and waiting times. We analyze the GOES
catalog with a statistical approach based on the comparison of the real catalog
with a reshuffled one where energies are decorrelated. This analysis reduces
the effect of background activity and is able to reveal the role of
obscuration. We show the existence of non-trivial correlations between waiting
times and energies, as well as between energies of subsequent flares. More
precisely, we find that flares close in time tend to have the second event with
large energy. Moreover, after large flares the flaring rate significantly
increases, together with the probability of other large flares. Results suggest
that correlations between energies and waiting times are a physical property
and not an effect of obscuration. These findings could give important
information on the mechanisms for energy storage and release in the solar
corona
The non-linear response of the magnetosphere: 30 October 1978
Previous efforts to find evidence of deterministic nonlinear dynamics in the
global geomagnetic system have treated the geomagnetic system as autonomous.
However, the geomagnetic system is strongly driven by the stochastic solar
wind. We consider the response of the magnetosphere, as given by the AE index,
for one day when the IMF had a nearly constant southward value. Using both a
series of non-linear statistics and non-linear prediction of the response to
the input signal , we find that there is some evidence for deterministic
non-linear response of the Earth's magnetosphere on that day.Comment: 4 pages, Postscript file compressed and uuencoded, made with uufiles
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Erfahrungen bei der Messung der Ergebnisqualität in der interventionellen Schmerztherapie
BACKGROUND There is a growing interest in patient-related outcome measurement. In this field questionnaires on touch screens are becoming more common. This study was designed to identify problems in usability and feasibility of a web-based questionnaire. STUDY PARTICIPANTS AND METHODS Patients who underwent a lumbar infiltration were recruited in 5 centers and 50 patients participated of which half were older than 62 years. One third of the patients had basically no former experience with computers or touch screens. The outcome was assessed before treatment and during follow-up on a simple web-based patient questionnaire, the Activity Index. Results were presented graphically and discussed during consultation. Patients, nurses and doctors were asked for standardized feedback. RESULTS Of the patients 84% completed the questionnaire in up to 6 min. An adapted form of the system usability scale (SUS) achieved an acceptance score of 71.8%. Problems in handling occurred mostly in older patients (>65 years). The system was scored with 72.9% and 78.5% in efficiency and handling, respectively, by the nurses. The attending physicians rated the usefulness and comprehensibility of the graphical representation of the results on average as 83.3% and both were scored neutral to positive; however, an average of 11.6% rated some aspects of the report to be suboptimal. CONCLUSION This web-based questionnaire is the first of its kind to be evaluated in everyday practice of interventional pain therapy for lumbar back pain. The vast majority of the patients were able to efficiently complete the questionnaire. The questionnaire was highly acceptable to patients, nurses and doctors. We found some usability problems but mainly in the older age group
Randomized clinical trial of the i-gelâ„¢ and Magill tracheal tube or single-use ILMAâ„¢ and ILMAâ„¢ tracheal tube for blind intubation in anaesthetized patients with a predicted difficult airway
Background The single-use supraglottic airway device i-gelâ„¢ has been described in several case reports as a conduit for intubation, but no prospective data about success rates of blind intubation are available. Therefore, we performed this prospective randomized controlled trial to compare the success rate of blind tracheal intubation with a Magill PVC tube through the i-gelâ„¢ with intubation using an sILMAâ„¢ PVC tube through the single-use intubating laryngeal mask airway (sILMAâ„¢). Methods With ethics committee approval and written informed consent, 80 patients with predictors of a difficult airway were computer randomized to either supraglottic airway device (SAD). The corresponding tracheal tube (TT) was introduced through the SAD under fibreoptic visualization but without fibreoptic guidance. Primary outcome was blind intubation success rate. Times, airway leak pressure, fibreoptic view, and adverse events were recorded. To control for the influence of the TT, we compared data from 40 patients described in an accompanying study (sILMAâ„¢ with Magill TT and i-gelâ„¢ with sILMAâ„¢ TT). Results Blind intubation success rate through the sILMAâ„¢ (69%) was higher than with the i-gelâ„¢ (15%, P<0.001). Data from the other patient group excluded the TT type as the primary cause for the difference in success rate. Removal of SADs was without problems with no difference between the type of SAD. Conclusions Blind tracheal intubation using the sILMAâ„¢ tube through the sILMAâ„¢ is much more successful than blind intubation with a Magill PVC tube through the i-gelâ„¢. Because of its low success rate, we would not recommend blind intubation through the i-gel
Statistics of finite-time Lyapunov exponents in the Ulam map
The statistical properties of finite-time Lyapunov exponents at the Ulam
point of the logistic map are investigated. The exact analytical expression for
the autocorrelation function of one-step Lyapunov exponents is obtained,
allowing the calculation of the variance of exponents computed over time
intervals of length . The variance anomalously decays as . The
probability density of finite-time exponents noticeably deviates from the
Gaussian shape, decaying with exponential tails and presenting spikes
that narrow and accumulate close to the mean value with increasing . The
asymptotic expression for this probability distribution function is derived. It
provides an adequate smooth approximation to describe numerical histograms
built for not too small , where the finiteness of bin size trimmes the sharp
peaks.Comment: 6 pages, 4 figures, to appear in Phys. Rev.
Performance assessment of a tightly baffled, long-legged divertor configuration in TCV with SOLPS-ITER
Numerical simulations explore the possibility to test the tightly baffled,
long-legged divertor (TBLLD) concept in a future upgrade of the Tokamak \`a
configuration variable (TCV). The SOLPS-ITER code package is used to compare
the exhaust performance of several TBLLD configurations with existing unbaffled
and baffled TCV configurations. The TBLLDs feature a range of radial gaps
between the separatrix and the outer leg side walls. All considered TBLLDs are
predicted to lead to a denser and colder plasma in front of the targets and
improve the power handling by factors of 2-3 compared to the present, baffled
divertor and by up to a factor of 12 compared to the original, unbaffled
configuration. The improved TBLLD performance is mainly due to a better neutral
confinement with improved plasma-neutral interactions in the divertor region.
Both power handling capability and neutral confinement increases when reducing
the radial gap. The core compatibility of TBLLDs with nitrogen seeding is also
evaluated and the detachment window with acceptable core pollution for the
proposed TBLLDs is explored, showing a reduction of required upstream impurity
concentration up to 18% to achieve the detachment with thinner radial gap
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