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Shock Models (shock + models)

Distribution by Scientific Domains
Physics and Astronomy75%

Selected Abstracts

In vivo behaviour of long-circulating liposomes in blood vessels in hamster inflammation and septic shock models,use of intravital fluorescence microscopy

LUMINESCENCE: THE JOURNAL OF BIOLOGICAL AND CHEMICAL LUMINESCENCE, Issue 2 2001
Jean-Marie Devoisselle
Abstract This study aimed to observe liposome uptake by leukocytes in vivo. The study was performed on skin by using a dorsal skin-fold chamber implanted in golden hamsters using intravital microscopy. 5 and 6-CF-encapsulated polyethylene glycolated liposomes were injected intravenously. The skin microcirculation was observed with an intravital Eclipse E800 Nikon microscope (using ×40, ×80 magnification) fitted with a Xenon light source and an epifluorescence assembly (excitation, 470,nm, FWHM 40,nm; emission, 540,nm, FWHM 40,nm). An ultra-high sensitivity videocamera mounted on the microscope projected the image onto a monitor, and the images (720,×,576 pixels) were recorded for playback analysis with a digital video cassette recorder. An acute inflammatory response was obtained by removing one complete layer of skin and the underlying fascia and avascular tissue on the opposing side of the flap corresponding to an area equivalent to the window aperture. Using this model and set-up, leukocyte rolling and adhesion were easily observed and the entry of PEGylated liposomes into hamster blood leukocytes was studied for a period of 6,h. PEGylated liposomes were clearly identified alone inside the blood flow and inside the leukocytes as soon as the inflammatory reaction appeared. This study shows for the first time that blood leukocytes in their natural milieu of whole blood are capable of interacting with, and taking up, liposomes. This observation is in accordance with previous in vitro studies. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Deep spectroscopy of the FUV,optical emission lines from a sample of radio galaxies at z, 2.5: metallicity and ionization,

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008
A. Humphrey
ABSTRACT We present long-slit near-infrared (NIR) spectra, obtained using the Infrared Spectrometer And Array Camera (ISAAC) instrument at the Very Large Telescope, which sample the rest-frame optical emission lines from nine radio galaxies at z, 2.5. One-dimensional spectra have been extracted and, using broad-band photometry, have been cross-calibrated with spectra from the literature to produce line spectra spanning a rest wavelength of ,1200,7000 Å. The resulting line spectra have a spectral coverage that is unprecedented for radio galaxies at any redshift. We have also produced a composite of the rest-frame ultraviolet (UV),optical line fluxes of powerful, z, 2.5 radio galaxies. We have investigated the relative strengths of Ly,, H,, H,, He ii,1640 and He ii,4687, and we find that Av can vary significantly from object to object. In addition, we have identified new line ratios to calculate electron temperature: [Ne v],1575/[Ne v],3426, [Ne iv],1602/[Ne iv],2423, O iii],1663/[O iii],5008 and [O ii],2471/[O ii],3728. We calculate an average O iii temperature of 14100+1000,600 K. We have modelled the rich emission line spectra, and we conclude that they are best explained by active galactic nucleus (AGN) photoionization with the ionization parameter U varying between objects. For shock models (with or without the precursor) to provide a satisfactory explanation for the data, an additional source of ionizing photons is required , presumably the ionizing radiation field of the AGN. Single slab photoionization models are unable to reproduce the high- and the low-ionization lines simultaneously: the higher ionization lines imply higher U than do the lower ionization lines. This problem may be alleviated either by combining two or more single slab photoionization models with different U, or by using mixed-medium models such as those of Binette, Wilson & Storchi-Bergmann. In either case, U must vary from object to object. On the basis of N v/N iv] and N iv]/C iv we argue that, while photoionization is the dominant ionization mechanism in the extended emission line regions (EELR), shocks make a fractional contribution (,10 per cent) to its ionization. The N v/N iv] and N iv]/C iv ratios in the broad-line region (BLR) of some quasars suggest that shock ionization may be important in the BLR also. We find that in the EELR of z, 2 radio galaxies the N/H abundance ratio is close to its solar value. We conclude that N/H and metallicity do not vary by more than a factor of 2 in our sample. These results are consistent with the idea that the massive ellipticals which become the hosts to powerful AGN are assembled very early in the history of the universe, and then evolve relatively passively up to the present day. [source]

H2 reformation in post-shock regions

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2010
H. M. Cuppen
ABSTRACT H2 formation is an important process in post-shock regions, since H2 is an active participant in the cooling and shielding of the environment. The onset of H2 formation therefore has a strong effect on the temperature and chemical evolution in the post-shock regions. We recently developed a model for H2 formation on a graphite surface in warm conditions. The graphite surface acts as a model system for grains containing large areas of polycyclic aromatic hydrocarbon structures. Here, this model is used to obtain a new description of the H2 formation rate as a function of gas temperature that can be implemented in molecular shock models. The H2 formation rate is substantially higher at high gas temperatures as compared to the original implementation of this rate in shock models, because of the introduction of H atoms which are chemically bonded to the grain (chemisorption). Since H2 plays such a key role in the cooling, the increased rate is found to have a substantial effect on the predicted line fluxes of an important coolant in dissociative shocks [O i] at 63.2 and 145.5 ,m. With the new model, a better agreement between the model and observations is obtained. Since one of the goals of Herschel/PACS will be to observe these lines with higher spatial resolution and sensitivity than the former observations by Infrared Space Observatory -LWS, this more accurate model is very timely to help with the interpretation of these future results. [source]