Search results for "Outflow"

Diagnostic accuracy of current sonographic criteria for the detection of outflow abnormalities in the internal jugular veins

2012

Objectives: This study was aimed at evaluation of the diagnostic value of Doppler sonography for the assessment of abnormalities in the internal jugular veins (IJVs). Method: One hundred and sixteen IJVs were assessed in 58 patients with associated multiple sclerosis. Findings of Doppler sonography were compared with results of the reference test: catheter venography. Results: At least one positive extracranial sonographic criterion suggesting venous abnormality was found in 92.2% of the assessed veins. Yet, sensitivity, specificity, positive and negative predictive values of sonography were low: 93.4%, 12.0%, 79.4% and 33.3% for at least one positive criterion, and for at least two positiv…

Extracranial Venous Drainage Pattern in Multiple Sclerosis and Healthy Controls: Application of the 2011 Diagnostic Criteria for Chronic Cerebrospina…

2015

The etiology of multiple sclerosis (MS) is still largely unknown and it has been proposed that an impaired venous drainage from the central nervous system, defined as chronic cerebrospinal venous insufficiency (CCSVI), may play a role in this. We investigated the prevalence of extracranial venous drainage pattern alterations in a cohort of MS patients based on the 2011 revised diagnostic criteria for CCSVI. Thirty-nine MS patients and 18 healthy subjects underwent blinded extra-cranial venous echo-color Doppler sonography to reveal the presence of CCSVI. There was no statistically significant difference between MS patients and healthy controls regarding CCSVI prevalence (p value = 0.53). Th…

Heart valve tissue engineering: how far is the bedside from the bench?

2015

Heart disease, including valve pathologies, is the leading cause of death worldwide. Despite the progress made thanks to improving transplantation techniques, a perfect valve substitute has not yet been developed: once a diseased valve is replaced with current technologies, the newly implanted valve still needs to be changed some time in the future. This situation is particularly dramatic in the case of children and young adults, because of the necessity of valve growth during the patient's life. Our review focuses on the current status of heart valve (HV) therapy and the challenges that must be solved in the development of new approaches based on tissue engineering. Scientists and physicia…

Special Uses of Viscoelastics

2000

The possibilities of viscoelastic use in phacoemulsification will be outlined in the following figures. Many ophthalmic surgeons apply viscoelastic substances in capsulorhexis to achieve a deep anterior chamber and extend the pupillary space (with a small pupil). Care must be taken during injection so that aqueous is permitted to flow out. When using a paracentesis to inject viscoelastic (Fig. 59), it must be big enough to allow aqueous outflow. For complete aqueous exchange in the anterior chamber, it is advisable to inject the viscoelastic into the opposite chamber angle.

EVIDENCE OF NON-THERMAL X-RAY EMISSION FROM HH 80

2013

Protostellar jets appear at all stages of star formation when the accretion process is still at work. Jets travel at velocities of hundreds of km s -1, creating strong shocks when interacting with the interstellar medium. Several cases of jets have been detected in X-rays, typically showing soft emission. For the first time, we report evidence of hard X-ray emission possibly related to non-thermal processes not explained by previous models of the post-shock emission predicted in the jet/ambient interaction scenario. HH 80 is located at the south head of the jet associated with the massive protostar IRAS 18162-2048. It shows soft and hard X-ray emission in regions that are spatially separate…

X-ray emission from stellar jets by collision against high-density molecular clouds: an application to HH 248

2015

We investigate the plausibility of detecting X-ray emission from a stellar jet that impacts against a dense molecular cloud. This scenario may be usual for classical T Tauri stars with jets in dense star-forming complexes. We first model the impact of a jet against a dense cloud by 2D axisymmetric hydrodynamic simulations, exploring different configurations of the ambient environment. Then, we compare our results with XMM-Newton observations of the Herbig-Haro object HH 248, where extended X-ray emission aligned with the optical knots is detected at the edge of the nearby IC 434 cloud. Our simulations show that a jet can produce plasma with temperatures up to 10 MK, consistent with producti…

Formation of X-ray emitting stationary shocks in magnetized protostellar jets

2016

X-ray observations of protostellar jets show evidence of strong shocks heating the plasma up to temperatures of a few million degrees. In some cases, the shocked features appear to be stationary. They are interpreted as shock diamonds. We aim at investigating the physics that guides the formation of X-ray emitting stationary shocks in protostellar jets, the role of the magnetic field in determining the location, stability, and detectability in X-rays of these shocks, and the physical properties of the shocked plasma. We performed a set of 2.5-dimensional magnetohydrodynamic numerical simulations modelling supersonic jets ramming into a magnetized medium and explored different configurations…

Stability analysis of relativistic jets from collapsars and its implications on the short-term variability of gamma-ray bursts

2002

We consider the transverse structure and stability properties of relativistic jets formed in the course of the collapse of a massive progenitor. Our numerical simulations show the presence of a strong shear in the bulk velocity of such jets. This shear can be responsible for a very rapid shear--driven instability that arises for any velocity profile. This conclusion has been confirmed both by numerical simulations and theoretical analysis. The instability leads to rapid fluctuations of the main hydrodynamical parameters (density, pressure, Lorentz factor, etc.). However, the perturbations of the density are effectively decoupled from those of the pressure because the beam of the jet is radi…

On the nature of the soft γ-ray emission in the hard state of the black hole transient GRS 1716-249

2020

The black hole transient GRS 1716-249 was monitored from the radio to the gamma-ray band during its 2016-2017 outburst. This paper focuses on the Spectral Energy Distribution (SED) obtained in 2017 February-March, when GRS 1716-249 was in a bright hard spectral state. The soft gamma-ray data collected with the INTEGRAL/SPI telescope show the presence of a spectral component which is in excess of the thermal Comptonisation emission. This component is usually interpreted as inverse Compton emission from a tiny fraction of non-thermal electrons in the X-ray corona. We find that hybrid thermal/non-thermal Comptonisation models provide a good fit to the X/gamma-ray spectrum of GRS 1716-249. The …

2019

Abstract. The evolution of the tropopause inversion layer (TIL) during cyclogenesis in the North Atlantic storm track is investigated using operational meteorological analysis data (Integrated Forecast System from the European Centre for Medium-Range Weather Forecasts). For this a total of 130 cyclones have been analysed during the months August through October between 2010 and 2014 over the North Atlantic. Their paths of migration along with associated flow features in the upper troposphere and lower stratosphere (UTLS) have been tracked based on the mean sea level pressure field. Subsets of the 130 cyclones have been used for composite analysis using minimum sea level pressure to filter t…