The spectra emitted from clouds near the Galactic Centre (GC) are investigated calculating the UV-optical-IR lines using the physical parameters and the element abundances obtained by the detailed ...modelling of mid-IR observations. Graphical representation of the spectra reveals strong lines. Characteristic line ratios calculated at the nebula provide information about the dereddened spectra emitted from regions near the GC. These line ratios are compared with those observed in active galaxies. We have found that the physical conditions in the nebulae near the GC are different from those of starburst galaxies and active galactic nuclei, namely, gas velocities and densities as well as the photoionization fluxes are relatively low. The geometrical thickness of the emitting filaments is particularly small suggesting that matter is strongly fragmented by instabilities leading to an underlying shock-generated turbulence. This is revealed by the power spectra of the radial velocities, of the mid-IR continuum flux and of the computed Si/H relative abundances. Moreover, turbulence could amplify the initial magnetic fields.
We compare the physical parameters and the relative abundances calculated throughout supernova (SN) and gamma -ray burst (GRB) host galaxies using a detailed modelling of the spectra. The coupled ...effect of shocks and radiation from the starburst within the host galaxy is considered. We have found the following. (i) Shock velocities are lower in long-period GRBs (LGRBs) than in SN host galaxies. (ii) O/H relative abundances in SN hosts are scattered within a range 8.0 < 12+log(O/H) < 8.85 but they are close to solar in LGRB hosts. LGRB galaxies hosting Wolf-Rayet stars have He/H = 0.13 in a few objects. (iii) The starburst temperatures within a few SN hosts are relatively high (T* > 10 super( 5) K). The values of T* in LGRB hosts are ~3-8 x 10 super( 4) K. (iv) The H alpha absolute flux calculated from the emitting clouds of a few SN hosts at 0.1 < z < 0.3 is sensibly higher than in the other galaxies. H alpha increases sharply with the ionization parameter U. The present analysis suggests that the SN-host symbiosis is stronger than for GRBs in terms of activity. The physical and chemical conditions in the GRB host galaxies are similar to those in starburst galaxies within a large redshift range.
Alveolar gas diffusion (DLCO) is impaired in chronic heart failure (CHF). Diffusion depends on membrane diffusion (DM) and the amount of blood participating in gas exchange (VC). How DM, VC, and the ...alveolar-capillary unit behave in relationship to CHF severity is unknown.
We measured pulmonary function, including DLCO, DM, VC, and alveolar volume (VA), in 191 CHF patients in NYHA class I-III. CHF patients were grouped accordingly to peak exercise oxygen uptake (pVO(2)): group <12 mL/min/kg (n=24), group 12-16 (n=76), group 16-20 (n=64), and group >20 (n=27). DLCO, DM, VC, and VA were lowest in severe CHF and were linearly related to pVO(2) (DLCO, r=0.577, P<0.001; DM, r=0.490, P<0.001; VC, r=0.216, P<0.01; VA, r=0.565, P<0.01). DM/VC ratio, an index of the alveolar-capillary unit efficiency, was higher in group <12 (0.49+/-0.39 mL/min/mmHg/mL) and >20 (0.46+/-0.29), compared with 12-16 (0.34+/-0.19) and 16-20 (0.35+/-0.17).
DLCO progressively worsens as CHF severity increases due to reduction in lung tissue participating to gas exchange (low VC and VA). In severe CHF, the few working alveolar-capillary units are the most efficient as shown by the high DM/VC. This is useful for maintaining gas exchange efficiency in severe CHF.
The latest observations of line and continuum spectra emitted from the extended narrow-line region (ENLR) of the Seyfert 2 galaxy NGC 7212 are analysed using models that account for photoionization ...from the active galactic nucleus (AGN) and shocks. The results show that relatively high (500–800 km s-1) shock velocities appear at the edge of the cone and beyond. The model-inferred AGN flux, which is lower than 10-11 photons cm-2 s-1 eV-1 at the Lyman limit, is more typical of low-luminosity AGN than Seyfert 2 galaxies. The preshock densities are characteristic of the ENLR and range between 80–150 cm-3. Nitrogen and sulphur are found to be depleted by a factor lower than 2, particularly at the eastern edge. Oxygen is depleted at several locations. The Fe/H ratio is approximately solar, whereas the Ne/H relative abundance is unusually high, 1.5–2 times the solar value. Modelling the continuum spectral energy distribution (SED), we have found radio synchrotron radiation generated by the Fermi mechanism at the shock front, whereas the X-rays are produced by the bremsstrahlung from a relatively high temperature plasma.
We explore the origin of the observed Lya and other ultraviolet (UV) lines from galaxies at z < 3.7 by detailed modelling of their spectra. The objects are chosen from among those showing (a) ...UV-optical-near-IR lines, (b) only UV lines and (c) Lya in the UV and a few optical lines. The total sample is heterogeneous, including galaxies in an all-sky radio survey, hard X-ray-emitting sources, a type 2 quasar (QSR)identified as a X-ray source, a type 2 active galactic nucleus (AGN) at high z (3.7), a very extended Lya-emitting nebula, objects in a multi-band imaging survey for Lyman-break galaxies and in a slitless spectroscopic survey for Lyman-alpha emitters (LAEs), etc. We also present UV line predictions for a sample of galaxies in the 0.0686 < z < 0.8829 range. For calculation of the line and continuum spectra, we use the code suma, which accounts consistently for photoionizing flux from an external source and shocks. Dust-reprocessed radiation is also calculated. The results show that calculated Lya/H beta values are generally higher than observed, except for a few starburst (SB)-dominated models. Some spectra are better reproduced by shock-dominated models. The sample of galaxies including the Lya line shows neither peculiar gas physical conditions nor abnormal element abundances. The line profiles have complex full widths at half maximum (FWHM) with two main components, which translate into two types of emitting gas clouds. High T* values (>105 K), which indicate that SB stars are close to outburst, were found in a few objects. Traces of supernova events are suggested by a scandium emission line from the SST24 nebula and by shock-dominated models.
A new method to evaluate the dust-to-gas ratios in the Kepler SNR is presented. Dust emission in the infrared and bremsstrahlung are calculated consistently, considering that dust grains are ...collisionally heated by the gas throughout the front and downstream of both the expanding and the reverse shocks. The calculated continuum SED is constrained by the observational data. The dust-to-gas ratios are determined by the ratio of the dust emission bump and bremsstrahlung in the infrared. The shell-like morphological similarity of X-ray and radio emission, and of images in Hα and in infrared wavelengths confirms that both radio and X-ray emissions are created at the front of the expanding shock and that dust and gas are coupled crossing the expanding and reverse shock fronts. The results show that large grains with radius of ~1 μm with dust-to-gas ratios <4 $\times$ 10-3 survive sputtering and are heated to a maximum temperature of 125 K downstream of the shock expanding outwards with a velocity of about 1000 $\rm km\,s^{-1}$. The high velocity shocks become radiative for dust-to-gas ratios >10-3. Such shocks do not appear in the NE region, indicating that dust grains are not homogeneously distributed throughout the remnant. Smaller grains with radius of about 0.2 μm and dust-to-gas ratios of ~4 $\times$ 10-4 are heated to a maximum temperature of ~50 K downstream of the reverse shock corresponding to velocities of about 50 $\rm km\,s^{-1}$. A maximum dust mass <0.16 $M_{\odot}$ is calculated.
We have collected continuum data of a sample of D-type symbiotic stars. By modelling their spectral energy distribution in a colliding-wind theoretical scenario we have found characteristics common ...to all the systems: (1) at least two dust shells are clearly present, one at ∼1000 K and the other at ∼400 K; they dominate the emission in the infrared; (2) the radio data are explained by thermal self-absorbed emission from the reverse shock between the stars; while (3) the data in the long wavelength tail come from the expanding shock outwards the system; (4) in some symbiotic stars, the contribution from the white dwarf in the UV is directly seen. Finally, (5) for some objects soft X-ray emitted by bremsstrahlung downstream of the reverse shock between the stars is predicted. The results thus confirm the validity of the colliding-wind model and the important role of the shocks. The comparison of the fluxes calculated at the nebula with those observed at the Earth reveals the distribution throughout the system of the different components, in particular the nebulae and the dust shells. The correlation of shell radii with the orbital period shows that larger radii are found at larger periods. Moreover, the temperatures of the dust shells regarding the sample are found at ∼1000 and ≤400 K, while in the case of late giants they spread more uniformly throughout the same range.
We investigate the properties of dust and dust-to-gas ratios in various starburst regions of luminous infrared galaxies (LIGs). We refer to the sample of seven LIGs recently observed in the ...mid-infrared by Soifer et al. using the Keck Telescope with spatial resolution approaching the diffraction limit. These seven objects are among the closest LIGs and have been classified as starburst galaxies from optical spectroscopy. Our goal consists in modelling the continuum spectral energy distribution of each galaxy, particularly in the infrared range. Models are further constrained by observed emission-line ratios in the optical range. Multicloud models consistently account for the coupled effects of shock, photoionization by hot stars and diffuse secondary radiation from the shock-heated gas. Emission from clouds in the neighbourhood of evolved starbursts and with high shock velocities (∼500 km s−1) explains both the bremsstrahlung and reradiation from dust in the mid-infrared. Clouds with lower velocity (100 km s−1), which correspond to younger starbursts, also contribute to both line and continuum spectra. Both low- and high-velocity clouds are thus present in nearly all the sample galaxies. For all the galaxies, an old stellar population is revealed by blackbody emission in the optical/near-infrared range. Dust-to-gas ratios vary in different regions of individual galaxies.
The complex mechanics of the gastric wall facilitates the main digestive tasks of the stomach. However, the interplay between the mechanical properties of the stomach, its microstructure, and its ...vital functions is not yet fully understood. Importantly, the pig animal model is widely used in biomedical research for preliminary or ethically prohibited studies of the human digestion system. Therefore, this study aims to thoroughly characterize the mechanical behavior and microstructure of the porcine stomach. For this purpose, multiple quasi-static mechanical tests were carried out with three different loading modes, i.e., planar biaxial extension, radial compression, and simple shear. Stress-relaxation tests complemented the quasi-static experiments to evaluate the deformation and strain-dependent viscoelastic properties. Each experiment was conducted on specimens of the complete stomach wall and two separate layers, mucosa and muscularis, from each of the three gastric regions, i.e., fundus, body, and antrum. The significant preconditioning effects and the considerable regional and layer-specific differences in the tissue response were analyzed. Furthermore, the mechanical experiments were complemented with histology to examine the influence of the microstructural composition on the macrostructural mechanical response and vice versa. Importantly, the shear tests showed lower stresses in the complete wall compared to the single layers which the loose network of submucosal collagen might explain. Also, the stratum arrangement of the muscularis might explain mechanical anisotropy during tensile tests. This study shows that gastric tissue is characterized by a highly heterogeneous microstructure with regional variations in layer composition reflecting not only functional differences but also diverse mechanical behavior. STATEMENT OF SIGNIFICANCE: Unfortunately, only few experimental data on gastric tissue are available for an adequate material parameter and model estimation. The present study therefore combines layer- and region-specific stomach wall mechanics obtained under multiple loading conditions with histological insights into the heterogeneous microstructure. On the one hand, the extensive data sets of this study expand our understanding of the interplay between gastric mechanics, motility and functionality, which could help to identify and treat associated pathologies. On the other hand, such data sets are of high relevance for the constitutive modeling of stomach tissue, and its application in the field of medical engineering, e.g., in the development of surgical staplers and the improvement of bariatric surgical interventions.
Shock fronts in the symbiotic system BI Crucis Contini, M.; Angeloni, R.; Rafanelli, P.
Monthly notices of the Royal Astronomical Society,
06/2009, Letnik:
396, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We investigate the symbiotic star BI Crucis (BI Cru) through a comprehensive and self-consistent analysis of the spectra emitted in three different epochs: 1960s, 1970s and late 1980s. In particular, ...we would like to find out the physical conditions in the shocked nebula and in the dust shells, as well as their location within the symbiotic system, by exploiting both photometric and spectroscopic data from radio to UV. We suggest a model which, on the basis of optical imaging, emission-line ratios and spectral energy distribution profile, is able to account for collision of the winds, formation of lobes and jets by accretion onto the white dwarf (WD), as well as for the interaction of the blast wave from a past, unrecorded outburst with the interstellar medium (ISM). We have found that the spectra observed throughout the years show the marks of the different processes at work within BI Cru, perhaps signatures of a post-outburst evolution. We then call for new infrared and millimeter observations, potentially able to resolve the inner structure of the symbiotic nebula.
PDF
