56 research outputs found

    Short-scale turbulent fluctuations driven by the electron-temperature gradient in the national spherical torus experiment

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    Measurements with coherent scattering of electromagnetic waves in plasmas of the National Spherical Torus Experiment indicate the existence of turbulent fluctuations in the range of wave numbers k(perpendicular to)rho(e)=0.1-0.4, corresponding to a turbulence scale length nearly equal to the collisionless skin depth. Experimental observations and agreement with numerical results from a linear gyrokinetic stability code support the conjecture that the observed turbulence is driven by the electron-temperature gradient.X1155sciescopu

    Utilisation of an operative difficulty grading scale for laparoscopic cholecystectomy

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    Background A reliable system for grading operative difficulty of laparoscopic cholecystectomy would standardise description of findings and reporting of outcomes. The aim of this study was to validate a difficulty grading system (Nassar scale), testing its applicability and consistency in two large prospective datasets. Methods Patient and disease-related variables and 30-day outcomes were identified in two prospective cholecystectomy databases: the multi-centre prospective cohort of 8820 patients from the recent CholeS Study and the single-surgeon series containing 4089 patients. Operative data and patient outcomes were correlated with Nassar operative difficultly scale, using Kendall’s tau for dichotomous variables, or Jonckheere–Terpstra tests for continuous variables. A ROC curve analysis was performed, to quantify the predictive accuracy of the scale for each outcome, with continuous outcomes dichotomised, prior to analysis. Results A higher operative difficulty grade was consistently associated with worse outcomes for the patients in both the reference and CholeS cohorts. The median length of stay increased from 0 to 4 days, and the 30-day complication rate from 7.6 to 24.4% as the difficulty grade increased from 1 to 4/5 (both p < 0.001). In the CholeS cohort, a higher difficulty grade was found to be most strongly associated with conversion to open and 30-day mortality (AUROC = 0.903, 0.822, respectively). On multivariable analysis, the Nassar operative difficultly scale was found to be a significant independent predictor of operative duration, conversion to open surgery, 30-day complications and 30-day reintervention (all p < 0.001). Conclusion We have shown that an operative difficulty scale can standardise the description of operative findings by multiple grades of surgeons to facilitate audit, training assessment and research. It provides a tool for reporting operative findings, disease severity and technical difficulty and can be utilised in future research to reliably compare outcomes according to case mix and intra-operative difficulty

    Population‐based cohort study of outcomes following cholecystectomy for benign gallbladder diseases

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    Background The aim was to describe the management of benign gallbladder disease and identify characteristics associated with all‐cause 30‐day readmissions and complications in a prospective population‐based cohort. Methods Data were collected on consecutive patients undergoing cholecystectomy in acute UK and Irish hospitals between 1 March and 1 May 2014. Potential explanatory variables influencing all‐cause 30‐day readmissions and complications were analysed by means of multilevel, multivariable logistic regression modelling using a two‐level hierarchical structure with patients (level 1) nested within hospitals (level 2). Results Data were collected on 8909 patients undergoing cholecystectomy from 167 hospitals. Some 1451 cholecystectomies (16·3 per cent) were performed as an emergency, 4165 (46·8 per cent) as elective operations, and 3293 patients (37·0 per cent) had had at least one previous emergency admission, but had surgery on a delayed basis. The readmission and complication rates at 30 days were 7·1 per cent (633 of 8909) and 10·8 per cent (962 of 8909) respectively. Both readmissions and complications were independently associated with increasing ASA fitness grade, duration of surgery, and increasing numbers of emergency admissions with gallbladder disease before cholecystectomy. No identifiable hospital characteristics were linked to readmissions and complications. Conclusion Readmissions and complications following cholecystectomy are common and associated with patient and disease characteristics

    Study of edge turbulence through correlation analysis of 2-D ECEI channels in the KSTAR

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    The measurement of a long wavelength (ky??s ??? 0.1) edge turbulence has been carried out using correlation study of the 2-D electron cyclotron emission imaging (ECEI) [1] data in KSTAR. The correlation technique provides a clear response to poloidal wavenumber in the range of &lt; 1cm&amp;#8722;1 and average group velocity of ??? 3 km/s with the electron diamagnetic direction during the ELM crash suppressed phase. Besides, the radial and poloidal size of turbulenct eddies are small compared to typical ELM flux tube and the parallel wavenumber of turbulence is in the range of 0.67 &lt; kk &lt; 6 m&amp;#8722;1. It is also applied to both L- and H-mode to compare the turbulence properties and the result shows that the turbulence features of the ELM crash suppression is similar to those of L-mode. In addition, the velocimetry technique [2] has been applied to ECE imaging data to yield time dependent 2-D velocity field of Te turbulence at the plasma edge in the ELM crash suppression phase

    Observation of edge turbulence spread by ECEI on the ELM-crash-suppressed plasmas in the KSTAR

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    The structure and dynamics of the ELM and edge turbulence modified by n=1 RMP have been studied during the ELM-crash-suppression phase by applying correlation analysis techniques on the measured ECEI signals. The ECEI shows that filamentary modes remained at theedge with frequent bursts during ELM-crash-suppression phase. The filamentary mode fluctuates in the range of 20 kHz and the dynamics of the mode seems to be violent and complex compared to the ELMing H-mode phase. Correlation analysis shows corresponding fluctuations have long poloidal wavelength (or small poloidal wavenumber k??&lt;1 cm&amp;#8722;1) with smaller size compared to the filamentary mode, and average group velocity of ???3 km/s along the electron diamagnetic direction, parallel wavelengths in the range of 2&lt;??||&lt;8 m. The characteristic size in the order of k????s???0.1 and velocimetry analysis suggest the resistive ballooning mode is a strong candidate for edge fluctuation in the ELM-crash-suppression phase

    Effect of edge turbulence on ELM-crash-suppression under n=1 RMP

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    The effect of n = 1 RMP on the edge-localized mode (ELM) and edge turbulence has been investigated by using electron cyclotron emission imaging (ECEI) system [1] in the KSTAR. The ECEI revealed that the filamentary structure of ELM is maintained with substantial fluctuation in amplitude without large scale collapse. Correlation analysis showed that the RMP enhances turbulent fluctuations in the edge toward the ELM-crashsuppression phase. The spectral power distribution of the turbulence has been obtained showing a linear dispersion for wide ranges of wavenumber (k?? &lt; 1 cm&amp;#8722;1) and frequency (&lt; 70 kHz). Velocimetry analysis [2] confirmed that the potential and density fluctuations of turbulent eddies are approximately out of phase and thus the turbulence involves a net radial transport. Bispectral analysis [3] clearly shows that the coexisting ELM and edge turbulence nonlinearly interact each other
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