“Bendy” stents help negotiate hairpin intracardiac curves

Simple transposition of the great arteries (TGA) occurs in 0.2 per 1000 live births. The condition is surgically repaired in the neonatal period by the arterial switch procedure (ASO) sometimes preceded by an atrial septostomy. The ASO involves transecting the great arteries and relocating them to the appropriate ventriculo-arterial (VA) connection with attachment of the disconnected coronary arteries to the aorta. In the process, the attachment of the pulmonary artery to the right ventricle involves the Le Compte manoeuvre and to achieve this the pulmonary arteries must be fully mobilised and sometimes the main pulmonary artery may require patch augmentation as well. Nevertheless, pulmonary artery stenosis (PAS) is one of the potential problems with the ASO. However, with improved surgical techniques, this has dropped from around 15% in the 1980s to less than 3%. Apart from surgical revision when PAS occurs, there are interventional options which include angioplasty and/or stent insertion. The latter is preferred in small children and works well in around 60% but may require repeat procedures. In older patients or when angioplasty fails, stent insertion can be considered. These procedures may involve negotiating tight bends in order to reach the site of stenosis. The passage of non-premounted stents may be problematic in such situations, especially with longer stents and tighter bends as they tend to slip off balloon. We describe several techniques that may facilitate such interventions, and these were utilised in an adolescent patient who had had ASO for TGA in the neonatal period. These included manually giving the mounted stent a slight bend in order to help the balloon-stent assembly negotiate hairpin bends.peer-reviewe

Effect of electron heating on self-induced transparency in relativistic intensity laser-plasma interaction

The effective increase of the critical density associated with the interaction of relativistically intense laser pulses with overcritical plasmas, known as self-induced transparency, is revisited for the case of circular polarization. A comparison of particle-in-cell simulations to the predictions of a relativistic cold-fluid model for the transparency threshold demonstrates that kinetic effects, such as electron heating, can lead to a substantial increase of the effective critical density compared to cold-fluid theory. These results are interpreted by a study of separatrices in the single-electron phase space corresponding to dynamics in the stationary fields predicted by the cold-fluid model. It is shown that perturbations due to electron heating exceeding a certain finite threshold can force electrons to escape into the vacuum, leading to laser pulse propagation. The modification of the transparency threshold is linked to the temporal pulse profile, through its effect on electron heating.Comment: 13 pages, 12 figures; fixed some typos and improved discussion of review materia

Coherent forward stimulated Brillouin scattering of a spatially incoherent laser beam in a plasma and its effect on beam spray

A statistical model for forward stimulated Brillouin scattering (FSBS) is developed for a spatially incoherent, monochromatic, laser beam propagating in a plasma. A threshold for the average power in a speckle is found, well below the self-focusing one, above which the laser beam spatial incoherence can not prevent the coherent growth of FSBS. Three-dimensional simulations confirm its existence and reveal the onset of beam spray above it. From these results, we propose a new figure of merit for the control of the propagation through a plasma of a spatially incoherent laser beam.Comment: submitted to PR

Random matrix approach in search for weak signals immersed in background noise

We present new, original and alternative method for searching signals coded in noisy data. The method is based on the properties of random matrix eigenvalue spectra. First, we describe general ideas and support them with results of numerical simulations for basic periodic signals immersed in artificial stochastic noise. Then, the main effort is put to examine the strength of a new method in investigation of data content taken from the real astrophysical NAUTILUS detector, searching for the presence of gravitational waves. Our method discovers some previously unknown problems with data aggregation in this experiment. We provide also the results of new method applied to the entire respond signal from ground based detectors in future experimental activities with reduced background noise level. We indicate good performance of our method what makes it a positive predictor for further applications in many areas.Comment: 15 pages, 16 figure

Transcatheter closure of Ventricular Septal defects in Malta : initial experience

Ventricular septal defects (VSD) consist of deficiencies of the wall separating the two ventricles. VSDs are the commonest congenital cardiac defects. Small VSDs rarely require intervention, however, larger defects cause ventricular volume overload with or without heart failure or pulmonary hypertension and may, therefore, require closure. Traditionally, closure has been an open heart surgical procedure. In recent years, various devices have been developed to close a wide variety of cardiac defects including atrial septal defects and patent arterial ducts through transcatheter interventional techniques. Recently, AGA Medical Corporation have introduced a range of Amplatzer VSD occluders which include specific devices for perimembranous (PM), muscular and post myocardial infarction (MI) VSDs. Atrial septal defect and patent foramen ovale closure has been carried out at St. Luke's Hospital in Malta for the past three years. This year, for the first time, we have closed three VSDs in three individuals; two children with large perimembranous defects and an elderly gentleman with a large post-MI VSD. This paper will discuss this technique and initial results.peer-reviewe

Roughness and Finite Size Effect in the NYSE Stock-Price Fluctuations

We consider the roughness properties of NYSE (New York Stock Exchange) stock-price fluctuations. The statistical properties of the data are relatively homogeneous within the same day but the large jumps between different days prevent the extension of the analysis to large times. This leads to intrinsic finite size effects which alter the apparent Hurst (H) exponent. We show, by analytical methods, that finite size effects always lead to an enhancement of H. We then consider the effect of fat tails on the analysis of the roughness and show that the finite size effects are strongly enhanced by the fat tails. The non stationarity of the stock price dynamics also enhances the finite size effects which, in principle, can become important even in the asymptotic regime. We then compute the Hurst exponent for a set of stocks of the NYSE and argue that the interpretation of the value of H is highly ambiguous in view of the above results. Finally we propose an alternative determination of the roughness in terms of the fluctuations from moving averages with variable characteristic times. This permits to eliminate most of the previous problems and to characterize the roughness in useful way. In particular this approach corresponds to the automatic elimination of trends at any scale.Comment: 13 pages, 11 fugure