Search results for " Shock"
showing 10 items of 691 documents
Crushing of interstellar gas clouds in supernova remnants. I. The role of thermal conduction and radiative losses
2005
We model the hydrodynamic interaction of a shock wave of an evolved supernova remnant with a small interstellar gas cloud like the ones observed in the Cygnus loop and in the Vela SNR. We investigate the interplay between radiative cooling and thermal conduction during cloud evolution and their effect on the mass and energy exchange between the cloud and the surrounding medium. Through the study of two cases characterized by different Mach numbers of the primary shock (M = 30 and 50, corresponding to a post-shock temperature $T\approx 1.7\times 10^6$ K and $\approx 4.7\times 10^6$ K, respectively), we explore two very different physical regimes: for M = 30, the radiative losses dominate the…
Analysis of the hydrodynamics of a periodically operated trickle-bed reactor—A shock wave velocity
2014
Abstract The relationship describing the shock wave velocity was formulated for the trickle-bed reactor operating at periodically changed feeding the bed with liquid phase. The values of shock wave velocity calculated from derived equations were compared with experimental values obtained for both fast and slow mode of base–pulse periodic liquid feeding and using liquids differing in physicochemical properties. A good agreement between these two sets of values of shock wave velocity was obtained. It has to be emphasized that the relationship (Eq. (26) ) derived in this study enables to estimate the values of the shock wave velocity when only mean values of variables of a process are known.
Modeling nonthermal emission from stellar bow shocks
2016
Context. Runaway O- and early B-type stars passing through the interstellar medium at supersonic velocities and characterized by strong stellar winds may produce bow shocks that can serve as particle acceleration sites. Previous theoretical models predict the production of high-energy photons by nonthermal radiative processes, but their efficiency is still debated. Aims: We aim to test and explain the possibility of emission from the bow shocks formed by runaway stars traveling through the interstellar medium by using previous theoretical models. Methods: We applied our model to AE Aurigae, the first reported star with an X-ray detected bow shock, to BD+43 3654, in which the observations fa…
Examination of the shock wave regular reflexion phenomenon in a rarefied supersonic plasma flow
2005
The flow properties of a low-pressure weakly ionized supersonic argon plasma jet are examined using Fabry–Perot interferometry and laser induced fluorescence spectroscopy. The flow velocity and equilibrium temperature measured at the torch nozzle exit are in close agreement with computational fluid dynamics calculations. The model also predicts the plasma flow to be in a rarefied regime. Departure from thermal equilibrium is indeed observed behind the nozzle where the parallel temperature differs significantly from the perpendicular temperature. The development of the axial velocity component along the jet center stream line reveals the occurrence of the shock wave regular reflexion phenome…
Accretion shock on CTTSs and its X-ray emission
2009
High spectral resolution X-ray observations of classical T Tauri stars (CTTSs) demonstrate the presence of plasma at T~2-3×10^6 K and ne~10^11-10^13 cm-3. Stationary models suggest that this emission is due to shock-heated accreting material. We address this issue by a 1-D hydrodynamic model of the impact of the accretion flow onto a chromosphere of a CTTS with the aim of investigating the stability of accretion shock and the role of the chromosphere. Our simulations include the effects of gravity, radiative losses from optically thin plasma, the thermal conduction and a detailed modeling of the stellar chromosphere. Here we present the results of a simulation based on the parameters of the…
The nearest X-ray emitting protostellar jet observed with HST
2009
The HH 154 jet coming from the YSO binary L1551 IRS5 is one of the closest (about 150 pc) astrophysical jet known. It is therefore a unique laboratory for studies of outflow mechanisms and of the shocks forming at the interaction front between the expanding material and the ambient medium. The substructures (knots) observed within the HH 154 jet were imaged in several spectral bands using the Hubble Space Telescope. This allows us to derive a simple characterization of the physical conditions in different structures as well as to measure the proper motion of the knots in the jet, their flux variability and shock emission over a time base of about ten years. These knots in the jet undergo si…
Shock oscillation model for quasi-periodic oscillations in stellar mass and supermassive black holes
2007
We numerically examine centrifugally supported shock waves in 2D rotating accretion flows around a stellar-mass (10M_sun) and a supermassive (10^6M_sun) black holes over a wide range of input accretion rates of 10^7 >\dot M/\dot M_E>10^{-4}. The resultant 2D-shocks are unstable with time and the luminosities show quasi-periodic oscillations (QPOs) with modulations of a factor of 2-3 andwith periods of a tenth seconds to several hours, depending on the black hole masses. The shock oscillation model may explain the intermediate frequency QPOs with 1-10 Hz observed in the stellar-mass black hole candidates and also suggest the existence of QPOs with the period of hours in AGNs. When the accret…
Shock-induced complex phase-space dynamics of strongly turbulent flows
2017
Shock waves have been thoroughly investigated during the last century in many different branches of physics. In conservative (Hamiltonian) systems the shock singularity is regularized by weak wave dispersion, thus leading to the formation of a rapidly and regular oscillating structure, usually termed in the literature dispersive shock wave (DSW), see e.g. [1]. Here, we show that this fundamental singular process of DSW formation can break down in a system of incoherent nonlinear waves. We consider the strong turbulent regime of a system of nonlocal nonlinear optical waves. We report theoretically and experimentally a characteristic transition: Strengthening the nonlocal character of the non…
Laboratory evidence for proton energization by collisionless shock surfing
2021
Charged particles can be accelerated to high energies by collisionless shock waves in astrophysical environments, such as supernova remnants. By interacting with the magnetized ambient medium, these shocks can transfer energy to particles. Despite increasing efforts in the characterization of these shocks from satellite measurements at Earth’s bow shock as well as powerful numerical simulations, the underlying acceleration mechanism or a combination thereof is still widely debated. Here we show that astrophysically relevant super-critical quasi-perpendicular magnetized collisionless shocks can be produced and characterized in the laboratory. We observe the characteristics of super-criticali…
Electromagnetically generated extracorporeal shock waves for gallstone lithotripsy: in vitro experiments and clinical relevance.
1989
. First generation shock wave sources have been proved to disintegrate gallstones effectively, but they require the immersion of the patient's body in a tank of water. A recently developed second generation shock wave source (Siemens-Lithostar, Erlangen, FRG) generates shock waves electromagnetically. It presents several novel features. In particular the waterbath can be omitted and due to lower shock wave pressure general anaesthesia is not required. In vitro studies showed that 36 out of 38 gallstones (11–30 mm in diameter) could be disintegrated. Two concrements resisting lithotripsy were pure white cholesterol stones. Independent of shape, size, and composition (cholesterol or pigment) …