| 1. |
- Ederle, Joerg, et al.
(författare)
-
Carotid artery stenting compared with endarterectomy in patients with symptomatic carotid stenosis (International Carotid Stenting Study): an interim analysis of a randomised controlled trial
- 2010
-
Ingår i: The Lancet. - 1474-547X. ; 375:9719, s. 985-997
-
Tidskriftsartikel (refereegranskat)abstract
- Background Stents are an alternative treatment to carotid endarterectomy for symptomatic carotid stenosis, but previous trials have not established equivalent safety and efficacy. We compared the safety of carotid artery stenting with that of carotid endarterectomy. Methods The International Carotid Stenting Study (ICSS) is a multicentre, international, randomised controlled trial with blinded adjudication of outcomes. Patients with recently symptomatic carotid artery stenosis were randomly assigned in a 1:1 ratio to receive carotid artery stenting or carotid endarterectomy. Randomisation was by telephone call or fax to a central computerised service and was stratified by centre with minimisation for sex, age, contralateral occlusion, and side of the randomised artery. Patients and investigators were not masked to treatment assignment. Patients were followed up by independent clinicians not directly involved in delivering the randomised treatment. The primary outcome measure of the trial is the 3-year rate of fatal or disabling stroke in any territory, which has not been analysed yet. The main outcome measure for the interim safety analysis was the 120-day rate of stroke, death, or procedural myocardial infarction. Analysis was by intention to treat (ITT). This study is registered, number ISRCTN25337470. Findings The trial enrolled 1713 patients (stenting group, n=855; endarterectomy group, n=858). Two patients in the stenting group and one in the endarterectomy group withdrew immediately after randomisation, and were not included in the ITT analysis. Between randomisation and 120 days, there were 34 (Kaplan-Meier estimate 4.0%) events of disabling stroke or death in the stenting group compared with 27 (3.2%) events in the endarterectomy group (hazard ratio [HR] 1.28, 95% CI 0.77-2.11). The incidence of stroke, death, or procedural myocardial infarction was 8.5% in the stenting group compared with 5.2% in the endarterectomy group (72 vs 44 events; HR 1.69, 1.16-2.45, p=0.006), Risks of any stroke (65 vs 35 events; HR 1.92, 1.27-2.89) and all-cause death (19 vs seven events; HR 2.76, 1.16-6.56) were higher in the stenting group than in the endarterectomy group. Three procedural myocardial infarctions were recorded in the stenting group, all of which were fatal, compared with four, all non-fatal, in the endarterectomy group. There was one event of cranial nerve palsy in the stenting group compared with 45 in the endarterectomy group. There were also fewer haematomas of any severity in the stenting group than in the endarterectomy group (31 vs 50 events; p=0.0197). Interpretation Completion of long-term follow-up is needed to establish the efficacy of carotid artery stenting compared with endarterectomy. In the meantime, carotid endarterectomy should remain the treatment of choice for patients suitable for surgery.
|
|
| 2. |
- Lim, H.D., et al.
(författare)
-
Effects of bevelled nozzles on standoff shocks in supersonic impinging jets
- 2019
-
Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638 .- 1626-3219. ; 94
-
Tidskriftsartikel (refereegranskat)abstract
- Moderately under-expanded jets issuing from a circular baseline and two bevelled circular nozzles impinging upon a perpendicular flat plate were experimentally studied. The effects of nozzle-pressure-ratio and separation distance variations on the standoff shock formations were investigated with schlieren visualizations and a visual hull based three-dimensional (3D) shock reconstruction technique to provide deeper insights into their 3D features. Across all flow configurations arising from the different combinations of these parameters, results indicated that the bevelled nozzles are effective in introducing asymmetry to the standoff shock geometries. Depending on the exact flow configuration, standoff shock locations may also undergo significant upstream displacements. In particular, the single-bevelled nozzle produces highly unsteady standoff shocks with asymmetric oscillation amplitudes along both side of the nozzle lip regions. Changes to the standoff shock key characteristics were observed to be sensitive towards the jet shock structures and reflection point modified by the bevelled nozzle exits. In particular, the strength and relative position of the reflection point are identified as the major contributing factors influencing the upstream static pressure distribution of the standoff shock, hence leading to the observed changes in the standoff shock behaviour.
|
|
| 3. |
- Lim, H. D., et al.
(författare)
-
Short-time proper orthogonal decomposition of time-resolved schlieren images for transient jet screech characterization
- 2020
-
Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638 .- 1626-3219. ; 107
-
Tidskriftsartikel (refereegranskat)abstract
- Short-time Proper Orthogonal Decomposition (POD) is proposed as an image-based technique to study the transient jet screech characteristics of moderately under-expanded supersonic jets emanating from a circular baseline and two bevelled nozzles. Time-resolved schlieren imaging of turbulent flow structures were performed with an ultrahigh-speed schlieren setup. Short-time POD was performed by systematically sampling image-series with a short time delay, performing PODs and applying spectral analyses on the first POD mode coefficients, and plotting the peak frequencies from the resulting PSDs into a peak frequency-occurrence count histogram. The results are in good agreement with the near-field noise spectra and wavelet transform analysis of the microphone measurements, which revealed intermittent jet screech occurrences at St=0.25 for both baseline and 30 degrees bevelled jets, while none was detected for the 60 degrees bevelled jet. In particular, the occurrence counts of the frequency bins is proposed as a suitable parameter to characterize the intermittent nature of jet screech, with the frequency bin revealing the jet screech frequency if present. The present study demonstrates the advantage of short-time POD analysis on time-resolved schlieren images over traditional image-based POD methods, which includes computational gains from parallelization, the ability to handle much larger datasets and revealing insights into a transient flow and noise phenomenon.
|
|
| 4. |
- Lim, H.D., et al.
(författare)
-
Visual-hull based 3D reconstruction of shocks in under-expanded supersonic bevelled jets.
- 2018
-
Ingår i: Experimental Thermal and Fluid Science. - : Elsevier BV. - 0894-1777. ; 99, s. 458-473
-
Tidskriftsartikel (refereegranskat)abstract
- Three-dimensional shock structures produced by Mach 1.45 supersonic bevelled jets were digitally reconstructedbased on schlieren photography and a voxel-based visual hull technique. By taking advantage of the strong edgefeatures commonly found in schlieren images of shock waves, the proposed technique demonstrates the possibilityof performing shock wave reconstruction in supersonic jet applications without prior knowledge of theglobal density or velocity field. Semi-synthetic camera parameters were introduced as a method to circumventcamera calibration issues faced in the reconstruction procedure. This is key to achieving accurate and highresolutionreconstructed shock waves for both axisymmetric and asymmetric test cases with an average of 2.5%error when validated against raw schlieren images. When applied to bevelled jets with non-uniform nozzle exitgeometries, an additional assumption was made to address the problem of schlieren line-of-sight blockage by thenon-conventional nozzle, and reconstruction errors were found to be larger near regions of poorer shock wavecontrast. Current results indicate that the technique is robust and fast during image calibration and processing,with accuracy of reconstructed shock waves in both conventional and non-conventional nozzles strongly dependenton shock wave contrast. Compared to existing techniques that can be used to reconstruct 3D shockstructures, the proposed technique has the advantage of being totally non-intrusive as compared to point orparticle-based measurements, requires significantly less computation than tomographic methods, offers highresolution reconstruction even with limited camera resolution and projected schlieren views, and is easy and costeffective to implement.
|
|
| 5. |
- Mariani, Raffaello, et al.
(författare)
-
A comparative study on the use of calibrated and rainbow schlieren techniques in axisymmetric supersonic jets
- 2019
-
Ingår i: Flow Measurement and Instrumentation. - : Elsevier BV. - 0955-5986 .- 1873-6998. ; 66, s. 218-228
-
Tidskriftsartikel (refereegranskat)abstract
- Detailed experimental comparisons had been conducted between calibrated and rainbow schlieren on perfectly-and under-expanded axisymmetric supersonic jets through a modified Z-type schlieren system. The techniques were implemented by using a weak lens in the field-of-view to provide calibration information for the extraction of quantitative density gradients from the experimental schlieren images. Sixth-order polynomial curve fits were obtained for both calibrated and rainbow schlieren respectively. The effects of light inhomogeneity caused by the mirrors and system diaphragm aperture had been evaluated for the colour images and results indicate that averaging the background hue is an acceptable approach for minimizing light variations with less than 2% experimental error. Density gradients as calculated via Abel transform have also been evaluated to validate the two different set-ups. Additionally, experimental results have been compared to validated numerical results and they show that calibrated schlieren is able to predict density gradients within 2% of the numerical results. This is significantly more superior to rainbow schlieren, where errors in the estimated density gradients are clOser to 20%. It is shown here that rainbow schlieren results are more adversely impacted by the system diaphragm aperture, especially for vertical light cut-off configuration. This is partly due to the loss of sensitivity of the schlieren system, as well as potential light diffusion caused by the filter.
|
|
| 6. |
- Mariani, Raffaello, 1981-, et al.
(författare)
-
A Preliminary Study On the Implementation of Rainbow Schlieren with a Single-Mirror System
- 2019
-
Ingår i: Proc. of the 32nd International Symposium on Shock Waves. - Singapore : Research Publishing Services.
-
Konferensbidrag (refereegranskat)abstract
- An experimental study has been conducted on the application of rainbowschlieren with a single-mirror schlieren system for the study of over- and moderatelyunder-expanded jets. The technique used a weak lens in the field-of-view to providecalibration information for the extraction of quantitative data. The calibration imagerequired post-processing procedures that take into account the double diffraction of thelight inherent to the schlieren system in use, resulting in an exploitable range of re-fraction angles of ±1.45e−3rad. Density gradients were calculated using Abel transformand compared to validated reference data. Results show an experimental uncertainty inthe predicted density gradients to be as low as ±2%, with an overall average of ±10%.These improvements over previous works can be attributed to the higher sensitivity ofthe present schlieren system.
|
|
| 7. |
- Mariani, Raffaello, Assistant Prof. 1981-, et al.
(författare)
-
On the application of non-standard rainbow schlieren technique upon supersonic jets
- 2020
-
Ingår i: Journal of Visualization. - : Springer Nature. - 1343-8875 .- 1875-8975. ; 23:3, s. 383-393
-
Tidskriftsartikel (refereegranskat)abstract
- Abstract: A quantitative rainbow schlieren study was conducted on an over-expanded jet at nozzle pressure ratio of 2.8, based on two different schlieren set-ups: the standard z-type and a single-mirror schlieren set-up. The technique used a single, weak focal-length lens placed in the field of view of the system to provide the calibration information required for the extraction of the quantitative data. In the case of the single-mirror set-up, the calibration image required further post-processing procedures to take into account the double refraction experienced by the light. Density gradients were calculated using Abel transform and compared to validated reference data. Results indicate that the single-mirror set-up is able to improve prediction of the density gradient field as compared to the standard z-type schlieren, due to its inherent property of higher sensitivity. The study has shown that the single-mirror set-up performs on average better than the standard z-type system, yielding an overall averaged error of ± 20%, with localized values as low as ± 5% where the shock cell structure is clearly defined, with respect to the validated reference data. At the same time, both systems perform poorly in regions where the flow structure displays poor image contrast. Graphic abstract: [Figure not available: see fulltext.].
|
|
| 8. |
- Wei, X. F., et al.
(författare)
-
Experimental Investigations of Screech Mitigation and Amplification by Beveled and Double-Beveled Nozzles
- 2022
-
Ingår i: Journal of Aerospace Engineering. - : American Society of Civil Engineers (ASCE). - 0893-1321 .- 1943-5525. ; 35:4
-
Tidskriftsartikel (refereegranskat)abstract
- An experimental study was conducted to investigate and compare the effects of beveled and double-beveled circular nozzles on supersonic jet screech at a nozzle pressure ratio of 5. In particular, near- and far-field microphone measurements and schlieren visualizations were utilized to look into selected acoustic and flow features associated with jet screech radiation. Results show that beveled nozzles eliminate jet screech by producing asymmetric shock structures and instability waves that are mismatched in phase and amplitude. In contrast, double-beveled nozzles produce symmetric shock structures and amplify screech intensity, even when jet mixing effects have been significantly enhanced. It is further observed that amplified jet screeches produced by double-beveled nozzles are highly unsteady and undergo nonperiodic and stochastic temporal variations. Last but not least, double-beveled nozzles also significantly impact screech peak noise locations and confer different changes along different measurement planes. The present study demonstrates that not all beveled-type nozzles are able to mitigate jet screech, with nonoptimal designs amplifying it instead.
|
|
| 9. |
- Wei, X. F., et al.
(författare)
-
Mitigation of under-expanded supersonic jet noise through stepped nozzles
- 2019
-
Ingår i: Journal of Sound and Vibration. - : Academic Press. - 0022-460X .- 1095-8568. ; 459
-
Tidskriftsartikel (refereegranskat)abstract
- An experimental investigation into noise reduction of supersonic jets through nozzle trailing-edge modifications was conducted, whereby far-field acoustic measurements were captured for two different stepped nozzles under two distinct under-expanded conditions. When compared to a baseline nozzle, results show that stepped nozzles lead to significant noise reductions at certain polar and azimuthal angles. In particular, a maximum noise reduction of 6 dB is observed for the longest stepped nozzle at a nozzle-pressure-ratio of 4 and 0 degrees azimuthal angle. Spectral analysis shows that the noise reduction is mainly due to reduction in broadband shock associated noise and elimination of jet screech phenomenon. Abrupt changes in nozzle lip lengths of the stepped nozzles appear to disrupt acoustic feedback loop, thus resulting in screech cessation. Qualitative schlieren imaging and quantitative schlieren measurements were subsequently performed to correlate the shock structures and density gradient fields with the resulting noise components. Unlike those produced by the baseline nozzle, shock structures generated by the stepped nozzles are highly irregular and the jet plumes undergo discernible deflections. Lastly, the reduction in broadband shock associated noise is related to the lower shock strengths, as demonstrated by the density gradient profiles.
|
|
| 10. |
- Wei, X. F., et al.
(författare)
-
Near- and Far-Field Acoustic Measurements for Stepped Nozzles at Over- and Perfectly-Expanded Supersonic Jet Flow Conditions
- 2020
-
Ingår i: Journal of Fluids Engineering. - : ASME International. - 0098-2202 .- 1528-901X. ; 142:11
-
Tidskriftsartikel (refereegranskat)abstract
- Detailed near- and far-field acoustic measurements were conducted for two circularstepped nozzles with 30 deg and 60 deg design inclinations at over- and perfectlyexpandedsupersonic jet flow conditions and compared to those for a circular nonsteppednozzle. Far-field acoustic results show that stepped nozzles play an insignificant role inaltering noise emissions at perfectly expanded condition. At an over-expanded condition,however, the longer stepped nozzle produces significant noise reductions at the sidelineand upstream quadrants, while the shorter stepped nozzle does not. Noise spectra analysisand Schlieren visualizations show that noise reduction can be primarily attributed tomitigations in the broadband shock-associated noise (BSAN), due to the ability of the longerstepped nozzle in suppressing shock strengths at downstream region. Near-fieldacoustic measurements reveal that the source region, as well as the intensity of turbulentand shock noises, are highly sensitive to the stepped nozzle configuration. Furthermore,BSAN seems to be eliminated by the longer stepped nozzle in near-field region due to theshock structure modifications.
|
|
