37 research outputs found
Transonic Galactic Outflows and Their Influences to the Chemical Evolution of Galaxies and Intergalactic Space
We have categorized possible transonic solutions of galactic outflows in the
gravitational potential of DMH and SMBH using the isothermal, spherically
symmetric and steady model. We conclude that the gravitational potential of
SMBH generates a new transonic branch while Tsuchiya et al. (2013) concluded
that the gravitational potential of DMH forms one transonic solution. Because
these two transonic solutions have different mass fluxes and starting points,
these solutions will make different influences to the star formation rate, the
evolution of galaxies, and the chemical evolution of the intergalactic medium.
Therefore, we conclude that the influence of galactic outflows to the
intergalactic medium depends not only on the mass distribution but also on the
selected transonic solution. In addition, we have estimated range of parameters
(KDMH; KBH) for actual galaxies. Moreover, it may be possible to estimate the
galactic mass distributions of DMH and SMBH applying the model to the observed
profile of the outflow velocity. Although it is difficult to determine the
velocity of hot gas in the galactic halos from the current X-ray observations,
but the next-generation X-ray observatory will be able to detect the detailed
profiles of outflow velocities.Comment: 6 pages, 3 figures, accepted for publication in AIP Conference
Proceeding
Continuous transition from fast magnetic reconnection to slow reconnection and change of the reconnection system structure
This paper analytically investigates a series of two-dimensional MHD
reconnection solutions over a wide variation of magnetic Reynolds number
(). A new series of solutions explains a continuous transition from
Petschek-like fast regime to a Sweet-Parker-like slow regime. The inflow region
is obtained from a Grad-Shafranov analysis used by Nitta et al. 2002 and the
outflow region from a shock-tube approximation used by Nitta 2004, 2006. A
single X-point (Petschek-like) solution forms for a sufficiently small
. As gradually increases, the solutions shifts to an X-O-X
solution with a magnetic island between two X-points. When increases
further, the island collapses to a new elongated current sheet with Y-points at
both ends (Sweet-Parker-like). These reconnection structures expand
self-similarly as time proceeds. As increases, the reconnection rate
and the reducible fraction of the initial magnetic energy of the system
decrease as power-law functions of .Comment: 19 pages, 12 figure
Polytropic transonic galactic outflows in a dark matter halo with a central black hole
Polytropic transonic solutions of spherically symmetric and steady galactic winds in the gravitational potential of a dark matter halo (DMH) with a supermassive black hole (SMBH) are studied. The solutions are classified in terms of their topological features, and the gravitational potential of the SMBH adds a new branch to the transonic solutions generated by the gravity of the DMH. The topological types of the transonic solutions depend on the mass distribution, the amount of supplied energy, the polytropic index Îł and the slope α of the DMH mass distribution. When α becomes larger than a critical value αc, the transonic solution types change dramatically. Further, our model predicts that it is possible for a slowly accelerating outflow to exist, even in quiescent galaxies with small Îł. This slowly accelerating outflow differs from those considered in many of the previous studies focusing on supersonic outflows in active star-forming galaxies. In addition, our model indicates that outflows in active star-forming galaxies have only one transonic point in the inner region (âŒ0.01 kpc). The locus of this transonic point does not strongly depend on Îł. We apply the polytropic model incorporating mass flux supplied by stellar components to the Sombrero galaxy, and conclude that it can reproduce the observed gas density and the temperature distribution well. This result differs significantly from the isothermal model, which requires an unrealistically large mass flux. Thus, we conclude that the polytropic model is more realistic than the isothermal model, and that the Sombrero galaxy can have a slowly accelerating outflow
Magnetic Reynolds number dependence of reconnection rate and flow structure of the self-similar evolution model of fast magnetic reconnection
This paper investigates Magnetic Reynolds number dependence of the
``self-similar evolution model'' (Nitta et al. 2001) of fast magnetic
reconnection. I focused my attention on the flow structure inside and around
the reconnection outflow, which is essential to determine the entire
reconnection system (Nitta et al. 2002). The outflow is consist of several
regions divided by discontinuities, e.g., shocks, and it can be treated by a
shock-tube approximation (Nitta 2004). By solving the junction conditions
(e.g., Rankine-Hugoniot condition), the structure of the reconnection outflow
is obtained. Magnetic reconnection in most astrophysical problems is
characterized by a huge dynamic range of its expansion ( for typical
solar flares) in a free space which is free from any influence of external
circumstances. Such evolution results in a spontaneous self-similar expansion
which is controlled by two intrinsic parameters: the plasma- and the
magnetic Reynolds number. The plasma- dependence had been investigated in
our previous paper. This paper newly clarifies the relation between the
reconnection rate and the inflow structure just outside the Petschek-like slow
shock: As the magnetic Reynolds number increases, strongly converging inflow
toward the Petschek-like slow shock forms, and it significantly reduces the
reconnection rate.Comment: 16 pages. to appear in ApJ (2006 Jan. 20 issue
Hyperoxemia and excess oxygen use in early acute respiratory distress syndrome : Insights from the LUNG SAFE study
Publisher Copyright: © 2020 The Author(s). Copyright: Copyright 2020 Elsevier B.V., All rights reserved.Background: Concerns exist regarding the prevalence and impact of unnecessary oxygen use in patients with acute respiratory distress syndrome (ARDS). We examined this issue in patients with ARDS enrolled in the Large observational study to UNderstand the Global impact of Severe Acute respiratory FailurE (LUNG SAFE) study. Methods: In this secondary analysis of the LUNG SAFE study, we wished to determine the prevalence and the outcomes associated with hyperoxemia on day 1, sustained hyperoxemia, and excessive oxygen use in patients with early ARDS. Patients who fulfilled criteria of ARDS on day 1 and day 2 of acute hypoxemic respiratory failure were categorized based on the presence of hyperoxemia (PaO2 > 100 mmHg) on day 1, sustained (i.e., present on day 1 and day 2) hyperoxemia, or excessive oxygen use (FIO2 ℠0.60 during hyperoxemia). Results: Of 2005 patients that met the inclusion criteria, 131 (6.5%) were hypoxemic (PaO2 < 55 mmHg), 607 (30%) had hyperoxemia on day 1, and 250 (12%) had sustained hyperoxemia. Excess FIO2 use occurred in 400 (66%) out of 607 patients with hyperoxemia. Excess FIO2 use decreased from day 1 to day 2 of ARDS, with most hyperoxemic patients on day 2 receiving relatively low FIO2. Multivariate analyses found no independent relationship between day 1 hyperoxemia, sustained hyperoxemia, or excess FIO2 use and adverse clinical outcomes. Mortality was 42% in patients with excess FIO2 use, compared to 39% in a propensity-matched sample of normoxemic (PaO2 55-100 mmHg) patients (P = 0.47). Conclusions: Hyperoxemia and excess oxygen use are both prevalent in early ARDS but are most often non-sustained. No relationship was found between hyperoxemia or excessive oxygen use and patient outcome in this cohort. Trial registration: LUNG-SAFE is registered with ClinicalTrials.gov, NCT02010073publishersversionPeer reviewe