Testing Observational Techniques with 3D MHD Jets in Clusters

Observations of X-ray cavities formed by powerful jets from AGN in galaxy cluster cores are commonly used to estimate the mechanical luminosity of these sources. We test the reliability of observationally measuring this power with synthetic X-ray observations of 3-D MHD simulations of jets in a galaxy cluster environment. We address the role that factors such as jet intermittency and orientation of the jets on the sky have on the reliability of observational measurements of cavity enthalpy and age. An estimate of the errors in these quantities can be made by directly comparing ``observationally'' derived values with values from the simulations. In our tests, cavity enthalpy, age and mechanical luminosity derived from observations are within a factor of two of the simulation values.Comment: 4 pages, 3 figures; to appear in proceedings of The Monster's Fiery Breath: Feedback in Galaxies, Groups, and Clusters (AIP conference series

Recurrent ~24 h Periods in RXTE ASM Data

Analysis of data from the Rossi X-ray Timing Explorer satellite's All Sky Monitor instrument for several X-ray binary sources has identified a recurrent \~24 h period. This period is sometimes highly significant, giving rise to the possibility of it being identified as an orbital or super-orbital period. Further analysis has revealed the same period in a number of other X-ray sources. As a result this period has been discounted as spurious, described variously as arising from daily variations in background levels and beating between the sampling period and long-term secular trends in the light curves. We present here an analysis of the spurious periods and show that the dominant mechanism is in fact spectral leakage of low-frequency power present in the light curves.Comment: 9 Pages, 10 figures, 1 table, submitted to PASA 20th December 2004. Added 1 page of text and 3 figures to clarify results and discussion. Resubmitted 16th May 2005. Accepted 25th June 200

Quantifying energetics and dissipation in magnetohydrodynamic turbulence

We perform a suite of two- and three-dimensional magnetohydrodynamic (MHD) simulations with the Athena code of the non-driven Kelvin-Helmholtz instability in the subsonic, weak magnetic field limit. Focusing the analysis on the non-linear turbulent regime, we quantify energy transfer on a scale-by-scale basis and identify the physical mechanisms responsible for energy exchange by developing the diagnostic known as spectral energy transfer function analysis. At late times when the fluid is in a state of MHD turbulence, magnetic tension mediates the dominant mode of energy injection into the magnetic reservoir, whereby turbulent fluid motions twist and stretch the magnetic field lines. This generated magnetic energy turbulently cascades to smaller scales, while being exchanged backwards and forwards with the kinetic energy reservoir, until finally being dissipated. Incorporating explicit dissipation pushes the dissipation scale to larger scales than if the dissipation were entirely numerical. For scales larger than the dissipation scale, we show that the physics of energy transfer in decaying MHD turbulence is robust to numerical effects.Comment: 23 pages, 20 figures, 4 tables, Accepted for publication in MNRA

Duplex ultrasound in aneurysm surveillance following endovascular aneurysm repair: a comparison with computed tomography aortography

ObjectivesCumulative radiation dose, cost, and increased demand for computed tomography aortography (CTA) suggest that duplex ultrasonography (DU) may be an alternative to CTA-based surveillance. We compared CTA with DU during endovascular aneurysm repair (EVAR) follow-up.MethodsPatients undergoing EVAR had clinical and radiological follow-up data entered in a prospectively maintained database. For the purpose of this study, the gold standard test for endoleak detection was CTA, and an endoleak detected on DU alone was assumed to be a false positive result. DU interpretation was performed independently of CTA and vice versa.ResultsOne hundred thirty-two patients underwent EVAR, of whom 117 attended for follow-up ranging from six months to nine years (mean, 32 months). Adequate aneurysm sac visualisation on DU was not possible in 1.7% of patients, predominantly due to obesity. Twenty-eight endoleaks were detected in 28 patients during follow-up. Of these, 24 were initially identified on DU (four false negative DU examinations), and eight had at least one negative CTA with a positive DU prior to diagnosis. Twenty-three endoleaks were type II in nature and three of these patients had increased sac size. There was one type I and four type III endoleaks. Two of these (both type III) had an increased sac size. Of 12 patients with increased aneurysm size of 5 mm or more at follow-up, five had an endoleak visible on DU, yet negative CTA and a further five had endoleak visualisation on both DU and CTA. Of six endoleaks which underwent re-intervention, all were initially picked up on DU. One of these endoleaks was never demonstrated on CTA and a further two had at least one negative CTA prior to endoleak confirmation. Positive predictive value for DU was 45% and negative predictive value 94%. Specificity of DU for endoleak detection was 67% when compared with CTA, because of the large number of false positive DU results. Sensitivity for DU was 86%, with all clinically significant endoleaks demonstrated on CTA also detected on DU.ConclusionDespite its low positive predictive value, we found DU to be a sensitive test for the detection of clinically significant endoleaks. Given concerns about cumulative radiation exposure and cost, and the surprisingly low sensitivity of CTA for endoleak detection in this series, selective CTA based on DU surveillance may be a more appropriate long-term strategy

Case series of iatrogenic coronary stent avulsion: a rare complication with varied management strategies

Background Coronary stent avulsion is a rare, infrequently reported complication of percutaneous coronary intervention (PCI) with no consensus on management options. Case summary This case series presents three descriptions of iatrogenic coronary stent avulsions, and three different bailout management strategies. All patients presented with acute coronary syndrome and required PCI. In the first case, a freshly implanted stent was entrapped in a coronary guidewire and avulsed upon withdrawal of the wire into the aortic sinus. In the second case, a staged procedure to implant a new stent was complicated by stent dislodgement and entanglement with a recently implanted stent leading to avulsion of both stents into the aortic sinus and resultant dissection to the coronary arteries. In the third case, following a successful stent implantation, the tip of the coronary guidewire was bound to the proximal edge of the stent resulting in avulsion of the newly implanted stent into the ascending aorta upon retraction of the wire at the end of the procedure. The first two patients were managed percutaneously, and the third surgically. All patients have had acceptable technical and clinical outcomes. Discussion In the absence of a consensus on best bailout management strategy, we discuss the mechanisms of and the potential management options for this rare, but serious, complication

Case series of iatrogenic coronary stent avulsion: a rare complication with varied management strategies

Background Coronary stent avulsion is a rare, infrequently reported complication of percutaneous coronary intervention (PCI) with no consensus on management options. Case summary This case series presents three descriptions of iatrogenic coronary stent avulsions, and three different bailout management strategies. All patients presented with acute coronary syndrome and required PCI. In the first case, a freshly implanted stent was entrapped in a coronary guidewire and avulsed upon withdrawal of the wire into the aortic sinus. In the second case, a staged procedure to implant a new stent was complicated by stent dislodgement and entanglement with a recently implanted stent leading to avulsion of both stents into the aortic sinus and resultant dissection to the coronary arteries. In the third case, following a successful stent implantation, the tip of the coronary guidewire was bound to the proximal edge of the stent resulting in avulsion of the newly implanted stent into the ascending aorta upon retraction of the wire at the end of the procedure. The first two patients were managed percutaneously, and the third surgically. All patients have had acceptable technical and clinical outcomes. Discussion In the absence of a consensus on best bailout management strategy, we discuss the mechanisms of and the potential management options for this rare, but serious, complication

Identifying continuous quality improvement publications: what makes an improvement intervention ‘CQI’?

Background: The term continuous quality improvement (CQI) is often used to refer to a method for improving care, but no consensus statement exists on the definition of CQI. Evidence reviews are critical for advancing science, and depend on reliable definitions for article selection. Methods: As a preliminary step towards improving CQI evidence reviews, this study aimed to use expert panel methods to identify key CQI definitional features and develop and test a screening instrument for reliably identifying articles with the key features. We used a previously published method to identify 106 articles meeting the general definition of a quality improvement intervention (QII) from 9427 electronically identified articles from PubMed. Two raters then applied a six-item CQI screen to the 106 articles. Results: Per cent agreement ranged from 55.7% to 75.5% for the six items, and reviewer-adjusted intra-class correlation ranged from 0.43 to 0.62. ‘Feedback of systematically collected data’ was the most common feature (64%), followed by being at least ‘somewhat’ adapted to local conditions (61%), feedback at meetings involving participant leaders (46%), using an iterative development process (40%), being at least ‘somewhat’ data driven (34%), and using a recognised change method (28%). All six features were present in 14.2% of QII articles. Conclusions: We conclude that CQI features can be extracted from QII articles with reasonable reliability, but only a small proportion of QII articles include all features. Further consensus development is needed to support meaningful use of the term CQI for scientific communication