Radio mode feedback: Does relativity matter? Perucho, Manel; Martí, José-María; Quilis, Vicent ...
Monthly notices of the Royal Astronomical Society. Letters,
10/2017, Letnik:
471, Številka:
1
Journal Article
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Abstract Radio mode feedback, associated with the propagation of powerful outflows in active galaxies, is a crucial ingredient in galaxy evolution. Extragalactic jets are well collimated and ...relativistic, both in terms of thermodynamics and kinematics. They generate strong shocks in the ambient medium, associated with observed hotspots, and carve cavities that are filled with the shocked jet flow. In this Letter, we compare the pressure evolution in the hotspot and the cavity generated by relativistic and classical jets. Our results show that the classical approach underestimates the cavity pressure by a factor ≥2 for a given shocked volume during the whole active phase. The tension between both approaches can only be alleviated by unrealistic jet flow densities or gigantic jet areas in the classical case. As a consequence, the efficiency of a relativistic jet heating the ambient is typically ∼20 per cent larger compared with a classical jet, and the heated volume is 2 to 10 times larger during the time evolution. This conflict translates into two substantially disparate manners, both spatially and temporal, of heating the ambient medium. These differences are expected to have relevant implications on the star formation rates of the host galaxies and their evolution.
The ever increasing size and complexity of data coming from simulations of cosmic structure formation demand equally sophisticated tools for their analysis. During the past decade, the art of object ...finding in these simulations has hence developed into an important discipline itself. A multitude of codes based upon a huge variety of methods and techniques have been spawned yet the question remained as to whether or not they will provide the same (physical) information about the structures of interest. Here we summarize and extent previous work of the 'halo finder comparison project': we investigate in detail the (possible) origin of any deviations across finders. To this extent, we decipher and discuss differences in halo-finding methods, clearly separating them from the disparity in definitions of halo properties. We observe that different codes not only find different numbers of objects leading to a scatter of up to 20 per cent in the halo mass and V
max function, but also that the particulars of those objects that are identified by all finders differ. The strength of the variation, however, depends on the property studied, e.g. the scatter in position, bulk velocity, mass and the peak value of the rotation curve is practically below a few per cent, whereas derived quantities such as spin and shape show larger deviations. Our study indicates that the prime contribution to differences in halo properties across codes stems from the distinct particle collection methods and - to a minor extent - the particular aspects of how the procedure for removing unbound particles is implemented. We close with a discussion of the relevance and implications of the scatter across different codes for other fields such as semi-analytical galaxy formation models, gravitational lensing and observables in general.
Galactic jets are powerful energy sources reheating the intracluster medium in galaxy clusters. Their crucial role in the cosmic puzzle, motivated by observations, has been established by a great ...number of numerical simulations excluding the relativistic nature of these jets. We present the first relativistic simulations of the very long-term evolution of realistic galactic jets. Unexpectedly, our results show no buoyant bubbles, but large cocoon regions compatible with the observed X-ray cavities. The reheating is more efficient and faster than in previous scenarios, and it is produced by the shock wave driven by the jet, that survives for several hundreds of Myr. Therefore, the X-ray cavities in clusters produced by powerful relativistic jets would remain confined by weak shocks for extremely long periods and their detection could be an observational challenge.
Simulation allows surgical trainees to acquire surgical skills in a safe environment. With the aim of reducing the use of animal experimentation, different alternative nonliving models have been ...pursued. However, one of the main disadvantages of these nonliving models has been the absence of arterial flow, pulsation, and the ability to integrate both during a procedure on a blood vessel. In the present report, we have introduced a microvascular surgery simulation training model that uses a fiscally responsible and replicable pulsatile flow system.
We connected 30 human placentas to a pulsatile flow system and used them to simulate aneurysm clipping and vascular anastomosis.
The presence of the pulsatile flow system allowed for the simulation of a hydrodynamic mechanism similar to that found in real life. In the aneurysm simulation, the arterial flow could be evaluated before and after clipping the aneurysm using a Doppler ultrasound system. When practicing anastomosis, the use of the pulsatile flow system allowed us to assess the vascular flow through the anastomosis, with verification using the Doppler ultrasound system. Leaks were manifested as “blood” pulsatile ejections and were more frequent at the beginning of the surgical practice, showing a learning curve.
We have provided a step-by-step guide for the assembly of a replicable and inexpensive pulsatile flow system and its use in placentas for the simulation of, and training in, performing different types of anastomoses and intracranial aneurysms surgery.
The number of present day massive galaxies that have survived untouched since their formation at high-z is an important observational constraint to the hierarchical galaxy formation models. Using ...three different semianalytical models based on the Millenium simulation, we quantify the expected fraction and number densities of the massive galaxies that form at z > 2 and have evolved in stellar mass less than 10% and 30%. We find that only a small fraction of the massive galaxies that already formed at z ~ 2 have remained almost unaltered since their formation (<2% with Delta Mlow */Mlow * < 0.1 and <8% with Delta Mlow */Mlow * < 0.3). These fractions correspond to the following number densities of massive relics in the present day universe: ~1.2 x 10 super(-6) Mpc super(-3) for Delta Mlow */Mlow * <0.1 and ~5.7 x 10 super(-6) Mpc super(-3) for Delta Mlow */Mlow * < 0.3. The observed number of relic candidates found in the nearby universe is rather uncertain today (with uncertainties up to a factor of ~100), preventing us from establishing firm conclusions about the ability of current theoretical expectations to predict such an important number.
Sedation During Neurocritical Care Vanaclocha, Nieves; Chisbert, Vicente; Quilis, Vicent ...
Journal of neuroanaesthesiology and critical care,
06/2019, Letnik:
6, Številka:
2
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Abstract
Sedation is an essential therapeutic strategy in the care of neurocritical patients. Intravenous sedative agents are the most widely used, with promising alternatives (dexmedetomidine, ...ketamine, and volatile agents) to propofol and midazolam arising. Studies designed to evaluate superiority and avoid biases are required. A neurological awakening test is safe in most patients. Potential risks and benefits of limiting deep sedation and daily interruption of sedation in these patients remain unclear. The aim of this review was to report recent clinical evidence on sedation in this subgroup of patients, focusing on its effects on clinical prognosis.
We use a three-dimensional hydrodynamical code to simulate the effect of energy injection on cooling flows in the intracluster medium. Specifically, we compare a simulation of a 1015-M⊙ cluster with ...radiative cooling only with a second simulation in which thermal energy is injected 31 kpc off-centre, over 64 kpc3 at a rate of for 50 Myr. The heat injection forms a hot, low-density bubble which quickly rises, dragging behind it material from the cluster core. The rising bubble pushes with it a shell of gas which expands and cools. We find the appearance of the bubble in X-ray temperature and luminosity to be in good qualitative agreement with recent Chandra observations of cluster cores. Toward the end of the simulation, at 600 Myr, the displaced gas begins to fall back toward the core, and the subsequent turbulence is very efficient at mixing the low- and high-entropy gas. The result is that the cooling flow is disrupted for up to ∼ 50 Myr after the injection of energy ceases. Thus this mechanism provides a very efficient method for regulating cooling flows, if the injection events occur with a 1:1 duty cycle.
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