Home About us Contact
|
Home About us Contact | ||
|
|
||
Shock Heating (shock + heating)
Selected AbstractsMultiple-Well, multiple-path unimolecular reaction systems.INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2001Vibrationally excited 2-methylhexyl radicals formed by shock wave activation or by chemical activation can isomerize by multiple pathways to form any of six stable isomers, can fragment by multiple CH and CC bond fission pathways, and can be collisionally stabilized. Master equation simulations of chemical activation and of shock wave activation are used to explore the generic behavior of this complicated coupled system. Selecting the argon pressure in chemical activation systems that produce the 2-methyl-1-hexyl radical isomer (1) can control the yield of specific isomers. Shock heating of 1 also shows a highly regular sequence of isomer formation. This regular behavior is because the first isomerization steps are faster than subsequent steps. Other radical isomers, such as 2-methyl-3-hexyl (3), do not show such regular behavior, because the first isomerization step is slower than subsequent steps. Incubation and unimolecular rate-constant fall-off are observed in the shock wave simulations. The unimolecular rate-constant fall-off for the coupled system produces low-pressure limiting rate constants proportional to [M]n, where n can be greater than unity. The fact that n can be greater than unity is a natural feature of multichannel coupled unimolecular reaction systems, but detection of the effect in experiments may be very demanding. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 246,261, 2001 [source] Shock heating in the group atmosphere of the radio galaxy B2 0838+32AMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2008Nazirah N. Jetha ABSTRACT We present Chandra and radio observations, and analysis of Sloan Digital Sky Survey data, of the radio galaxy B2 0838+32A (4C 32.26) and its environment. The radio galaxy is at the centre of a nearby group that has often been identified with the cluster Abell 695, but we argue that the original Abell cluster is likely to be an unrelated and considerably more distant system. The radio source is a restarting radio galaxy and, using our Chandra data, we argue that the currently active lobes are expanding supersonically, driving a shock with Mach number 2.4+1.0,0.5 into the interstellar medium. This would be only the third strong shock round a young radio source to be discovered, after Centaurus A and NGC 3801. However, in contrast to both these systems, the host galaxy of B2 0838+32A shows no evidence for a recent merger, while the active galactic nuclei (AGN) spectrum shows no evidence for the dusty torus that would imply a large reservoir of cold gas close to the central black hole. On the contrary, the AGN spectrum is of a type that has been associated with the presence of a radiatively inefficient accretion flow that could be controlled by an AGN heating and subsequent cooling of the hot, X-ray emitting gas. If correct, this means that B2 0838+32A is the first source in which we can directly see entropy-increasing processes (shocks) driven by accretion from the hot phase of the interstellar medium. [source] Heating effects of the matrix of experimentally shocked Murchison CM chondrite: Comparison with micrometeoritesMETEORITICS & PLANETARY SCIENCE, Issue 1 2007Naotaka TOMIOKA However, if a major fraction of micrometeorites are produced by impacts on porous asteroids, they may have experienced shock heating before contact with the Earth's atmosphere (Tomeoka et al. 2003). A transmission electron microscope (TEM) study of the matrix of Murchison CM chondrite experimentally shocked at pressures of 10,49 GPa shows that its mineralogy and texture change dramatically, mainly due to shock heating, with the progressive shock pressures. Tochilinite is completely decomposed to an amorphous material at 10 GPa. Fe-Mg serpentine is partially decomposed and decreases in amount with increasing pressure from 10 to 30 GPa and is completely decomposed at 36 GPa. At 49 GPa, the matrix is extensively melted and consists mostly of aggregates of equigranular grains of Fe-rich olivine and less abundant low-Ca pyroxene embedded in Si-rich glass. The mineralogy and texture of the shocked samples are similar to those of some types of micrometeorites. In particular, the samples shocked at 10 and 21 GPa are similar to the phyllosilicate (serpentine)-rich micrometeorites, and the sample shocked at 49 GPa is similar to the olivine-rich micrometeorites. The shock heating effects also resemble the effects of pulse-heating experiments on the CI and CM chondrite matrices that were conducted to simulate atmospheric entry heating. We suggest that micrometeorites derived from porous asteroids are likely to go through both shock and atmospheric-entry heating processes. [source] The impact of mergers on relaxed X-ray clusters , III.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2008Effects on compact cool cores ABSTRACT We use the simulations presented in Poole et al. to examine the effects of mergers on the properties of cool cores in X-ray clusters. Motivated by recent Chandra and XMM,Newton observations, we propose a scheme for classifying the morphology of clusters based on their surface brightness and entropy profiles. Three dominant morphologies emerge: two hosting compact cores and central temperatures which are cool [CCC (compact cool core) systems] or warm [CWC (compact warm core) systems] and one hosting extended cores which are warm [EWC (extended warm core) systems]. In the cases we have studied, CCC states are disrupted only after direct collisions with merging cluster cores. This can happen in head-on collisions or during second pericentric passage in off-axis mergers. By the time they are relaxed, our remnant cores have generally been heated to warm core (CWC or EWC) states but subsequently recover CCC states by the end of the simulation. The only case resulting in a long-lived EWC state is a slightly off-axis 3:1 merger for which the majority of shock heating occurs during the accretion of a low-entropy stream formed from the disruption of the secondary's cool core. Since tdyn,tcool for all our relaxing merger remnant cores, compression prevents their core temperatures from falling until after they relax to the compact states allowed by their remnant central entropies. This naturally explains the population of relaxed CWC systems observed in recent Chandra and XMM,Newton observations with no need to invoke active galactic nuclei feedback. The morphological segregation in the Lx,Tx scaling relation noted by McCarthy et al. is qualitatively reflected in the results of our mergers as well. However, none of the cases we have studied produces systems with sufficiently high central entropies to account for the most underluminous EWC systems observed. Lastly, mergers do not efficiently mix the intracluster medium in our simulations. As a result, merging systems which initially host central metallicity gradients do not yield merger remnants with flat metallicity profiles. Taken together, these results suggest that once formed, compact core systems are remarkably stable against disruption from mergers. It remains to be demonstrated exactly how the sizable observed population of extended core systems was formed. [source] Radial distribution and strong lensing statistics of satellite galaxies and substructure using high-resolution ,CDM hydrodynamical simulationsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006Andrea V. Macciò ABSTRACT We analyse the number density and radial distribution of substructures and satellite galaxies using cosmological simulations that follow the gas dynamics of a baryonic component, including shock heating, radiative cooling and star formation within the hierarchical concordance Lambda cold dark matter model. We find that the dissipation of the baryons greatly enhances the survival of subhaloes, especially in the galaxy core, resulting in a radial distribution of satellite galaxies that closely follows the overall mass distribution. Hydrodynamical simulations are necessary to resolve the adiabatic contraction and dense cores of galaxies, resulting in a total number of satellites a factor of 2 larger than that found in pure dark matter simulation, in good agreement with the observed spatial distribution of satellite galaxies within galaxies and clusters. Convergence tests show that the cored distribution found by previous authors in pure N -body simulations was due to the physical overmerging of dark matter only structures. We proceed to use a ray-shooting technique in order to study the impact of these additional substructures on the number of violations of the cusp caustic magnification relation. We develop a new approach to try to disentangle the effect of substructures from the intrinsic discreteness of N -body simulations. Even with the increased number of substructures in the centres of galaxies, we are not able to reproduce the observed high numbers of discrepancies observed in the flux ratios of multiply lensed quasars. [source] | ||||||||||