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Search Results: 1 - 10 of 4067 matches for " Johannes Hensler "
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Mild hypothermia alone or in combination with anesthetic post-conditioning reduces expression of inflammatory cytokines in the cerebral cortex of pigs after cardiopulmonary resuscitation
Patrick Meybohm, Matthias Gruenewald, Kai D Zacharowski, Martin Albrecht, Ralph Lucius, Nikola F?sel, Johannes Hensler, Karina Zitta, Berthold Bein
Critical Care , 2010, DOI: 10.1186/cc8879
Abstract: Thirty pigs (28 to 34 kg) were subjected to cardiac arrest following temporary coronary artery occlusion. After seven minutes of ventricular fibrillation and two minutes of basic life support, advanced cardiac life support was started according to the current American Heart Association guidelines. Return of spontaneous circulation was achieved in 21 animals who were randomized to either normothermia at 38°C, hypothermia at 33°C or hypothermia at 33°C combined with sevoflurane (each group: n = 7) for 24 hours. The effects of hypothermia and the combination of hypothermia with sevoflurane on cerebral inflammatory response after cardiopulmonary resuscitation were studied using tissue samples from the cerebral cortex of pigs euthanized after 24 hours and employing quantitative RT-PCR and ELISA techniques.Global cerebral ischemia following resuscitation resulted in significant upregulation of cerebral tissue inflammatory cytokine mRNA expression (mean ± SD; interleukin (IL)-1β 8.7 ± 4.0, IL-6 4.3 ± 2.6, IL-10 2.5 ± 1.6, tumor necrosis factor (TNF)α 2.8 ± 1.8, intercellular adhesion molecule-1 (ICAM-1) 4.0 ± 1.9-fold compared with sham control) and IL-1β protein concentration (1.9 ± 0.6-fold compared with sham control). Hypothermia was associated with a significant (P < 0.05 versus normothermia) reduction in cerebral inflammatory cytokine mRNA expression (IL-1β 1.7 ± 1.0, IL-6 2.2 ± 1.1, IL-10 0.8 ± 0.4, TNFα 1.1 ± 0.6, ICAM-1 1.9 ± 0.7-fold compared with sham control). These results were also confirmed for IL-1β on protein level. Experimental settings employing hypothermia in combination with sevoflurane showed that the volatile anesthetic did not confer additional anti-inflammatory effects compared with hypothermia alone.Mild therapeutic hypothermia resulted in decreased expression of typical cerebral inflammatory mediators after cardiopulmonary resuscitation. This may confer, at least in part, neuroprotection following global cerebral ischemia and resuscitation.Althoug
Morphological Mutations of Dwarf Galaxies
Gerhard Hensler
Physics , 2012, DOI: 10.1007/978-3-642-22018-0_8
Abstract: Dwarf galaxies (DGs) are extremely challenging objects in extragalactic astrophysics. They are expected to originate as the first units in Cold Dark-Matter cosmology. They are the galaxy type most sensitive to environmental influences and their division into multiple types with various properties have invoked the picture of their variant morphological transformations. Detailed observations reveal characteristics which allow to deduce the evolutionary paths and to witness how the environment has affected the evolution. Here we review peculiarities of general morphological DG types and refer to processes which can deplete gas-rich irregular DGs leading to dwarf ellipticals, while gas replenishment implies an evolutionary cycling. Finally, as the less understood DG types the Milky Way satellite dwarf spheroidal galaxies are discussed in the context of transformation.
The Supernova-ISM/Star formation Interplay
Gerhard Hensler
Physics , 2014, DOI: 10.1017/S1743921313009575
Abstract: Supernovae are the most energetic stellar events and influence the interstellar medium by their gasdynamics and energetics. By this, both also affect the star formation positively and negatively. In this paper, we review the complexity of investigations aiming at understanding the interchange between supernova explosions with the star-forming molecular clouds. Commencing from analytical studies the paper advances to numerical models of supernova feedback from superbubble scales to galaxy structure. We also discuss parametrizations of star-formation and supernova-energy transfer efficiencies. Since evolutionary models from the interstellar medium to galaxies are numerous and are applying multiple recipes of these parameters, only a representative selection of studies can be discussed here.
The Morphological Origin of Dwarf Galaxies
Gerhard Hensler
Physics , 2011, DOI: 10.1051/eas/1148086
Abstract: Dwarf galaxies (DGs) serve as extremely challenging objects in extragalactic astrophysics. Their origin is expected to be set as the first units in CDM cosmology. Nevertheless they are the galaxy type most sensitive to environmental in uences and their division into multiple types with various properties have invoked the picture of their variant morphological transformations. Detailed observations reveal characteristics which allow to deduce the evolutionary paths and to witness how the environment has a?ected the evolution. Here we refer to general morphological DG types and review some general processes, most of which deplete gas-rich irregular DGs. Moreover, the variety of pecularities is brie y refered, but cannot be comprehensively analyzed because of limited paper space.
Supernova Feedback on the Interstellar Medium and Star Formation
Gerhard Hensler
Physics , 2010, DOI: 10.1017/S1743921311000561
Abstract: Supernovae are the most energetic stellar events and influence the interstellar medium by their gasdynamics and energetics. By this, both also affect the star formation positively and negatively. In this paper, we review the development of the complexity of investigations aiming at understanding the interchange between supernovae and their released hot gas with the star-forming molecular clouds. Commencing from analytical studies the paper advances to numerical models of supernova feedback from superbubble scales to galaxy structure. We also discuss parametrizations of star-formation and supernova-energy transfer efficiencies. Since evolutionary models from the interstellar medium to galaxies are numerous and apply multiple recipes of these parameters, only a representative selection of studies can be discussed here.
Massive stars and their environment: light and shadows
Tim Freyer,Gerhard Hensler
Revista mexicana de astronomía y astrofísica , 2000,
Abstract: Estudiamos, con un c odigo 2D de hidrodin amica radiativa, la interacci on de una estrella de 60M con el medio interestelar circundante. En algunos momentos de la evoluci on la regi on H II interacciona fuertemente con la burbuja formada por el viento estelar, requiriendo la inclusi on de la radiaci on ionizante y el viento estelar para describir apropiadamente al medio circunestelar. Se forman un amplia variedad de estructuras interesantes como nubes, cascarones y dedos. Tambi en presentamos la evoluci on temporal de la ionizaci on y la energ a cin etica del gas interestelar.
The effect of clouds on the dynamical and chemical evolution of gas-rich dwarf galaxies
S. Recchi,G. Hensler
Physics , 2009, DOI: 10.1002/asna.200911261
Abstract: We study the effects of clouds on the dynamical and chemical evolution of gas-rich dwarf galaxies, in particular focusing on two model galaxies similar to IZw18 and NGC1569. We consider both scenarios, clouds put at the beginning of the simulation and continuously created infalling ones. Due to dynamical processes and thermal evaporation, the clouds survive only a few tens of Myr, but during this time they act as an additional cooling agent and the internal energy of cloudy models is typically reduced by 20 - 40% in comparison with models without clouds. The clouds delay the development of large-scale outflows, therefore helping to retain a larger amount of gas inside the galaxy. However, especially in models with continuous creation of infalling clouds, their bullet effect can pierce the expanding supershell and create holes through which the superbubble can vent freshly produced metals. Moreover, assuming a pristine chemical composition for the clouds, their interaction with the superbubble dilutes the gas, reducing the metallicity (by up to ~ 0.4 dex) with respect to the one attained by diffuse models.
Modelling the chemical evolution
Gerhard Hensler,Simone Recchi
Physics , 2010, DOI: 10.1017/S1743921310000815
Abstract: Advanced observational facilities allow to trace back the chemical evolution of the Universe, on the one hand, from local objects of different ages and, secondly, by direct observations of redshifted objects. The chemical enrichment serves as one of the cornerstones of cosmological evolution. In order to understand this chemical evolution in morphologically different astrophysical objects models are constructed based on analytical descriptions or numerical methods. For the comparison of their chemical issues, as there are element abundances, gradients, and ratios, with observations not only the present-day values are used but also their temporal evolution from the first era of metal enrichment. Here we will provide some insight into basics of chemical evolution models, highlight advancements, and discuss a few applications.
Chemical Abundance Ratios and Gas-Phase Mixing in Dwarf Galaxy Evolution
G. Hensler,A. Rieschick
Physics , 1998,
Abstract: Because of their low gravitational energies dwarf galaxies are greatly exposed to energetical influences by the interstellar medium, like e.g.\ stellar radiation, winds or explosions, or by their environment. While the metallicity depletion in dwarf galaxies can be explained in general by supernova-driven galactic winds, the reason for their low N/O ratios at low O abundance is not yet completely understood. Stellar yields enrich the different gas phases with elements that are characteristic for the stellar progenitors. Phase transitions are necessary for a mixing of elements, but depend sensitively on the thermal and dynamical state of the interstellar medium. Models of chemical evolution start usually with a high N/O ratio at low O abundance according to a metal enrichment by ancient stellar populations with common yields, but can only reproduce the N/O-O peculiarity by the application of multiple starbursts. Their galactic winds are invoked to reduce O selectively. Chemodynamical models of dwarf galaxies, however, demonstrate that strong evaporation of clouds by the hot supernova gas leads to an almost perfect mixing of the interstellar gas. These models can successfully account for the observed N/O-O values in a self-consistent way without the necessity of starbursts, if new stellar yields are taken into account which provide additional secondary N production from massive stars.
Chemodynamical gas flow cycles and their influence on the chemical evolution of dwarf irregular galaxies
Andreas Rieschick,Gerhard Hensler
Physics , 2003, DOI: 10.1023/A:1024081708806
Abstract: Here we investigate an exemplary chemodynamical evolutionary simulation of a dwarf irregular galaxy. By means of this model we demonstrate the existence of three gas mixing cycles: 1) An inner "local cycle" mixing the metals produced in stars locally, and 2) an outer "galactic cycle" on which hot gas is driven out of the galaxy by multiple supernovae type II and mixes on a short timescale with the available cold gas. 3) Only a small fraction of the metals leaves the galactic gravitational field and follows the "global cycle" with the intergalactic matter. The large-scale mixing results in a temporary depletion of supernova ejected metals. We will discuss this "delayed recycling" and its influence on the chemical evolution, especially on the nitrogen over oxygen ratio which is increased temporarily. These results presented her are also relevant for less sophisticated analytical approaches and chemical evolutionary models of galaxies which have to parameterize the metal loss through outflow.
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