8,053 research outputs found
Radiation induced precursor flow field ahead of a Jovian entry body
The change in flow properties ahead of the bow shock of a Jovian entry body, resulting from absorption of radiation from the shock layer, is investigated. Ultraviolet radiation is absorbed by the free stream gases, causing dissociation, ionization, and an increase in enthalpy of flow ahead of the shock wave. As a result of increased fluid enthalpy, the entire flow field in the precursor region is perturbed. The variation in flow properties is determined by employing the small perturbation technique of classical aerodynamics as well as the thin layer approximation for the preheating zone. By employing physically realistic models of radiative transfer, solutions are obtained for velocity, pressure, density, temperature, and enthalpy variations. The results indicate that the precursor flow effects, in general, are greater at higher altitudes. Just ahead of the shock, however, the effects are larger at lower altitudes. Pre-heating of the gas significantly increases the static pressure and temperature ahead of the shock for velocities exceeding 36 km/sec
Influence of precursor heating on viscous flow around a Jovian entry body
The influence of changes in precursor region flow properties (resulting from the absorption of radiation from the shock layer) on the entire shock layer flow phenomena was investigated. The axially symmetric case is considered for both the preheating zone (precursor region) and shock layer. The flow in the shock layer is assumed to be viscous with chemical equilibrium but radiative nonequilibrium. Realistic thermophysical and spectral models are employed, and results are obtained by implicit finite difference and iterative procedures. The results indicate that precursor heating increases the radiative heating of the body by a maximum of 7.5 percent for 116 km entry conditions
Effects of precursor heating on radiative and chemically reacting viscous flow around a Jovian entry body
The influence of change in the precursor region flow properties on the entire shock layer flow phenomena around a Jovian entry body was investigated. The flow in the shock layer was assumed to be steady, axisymmetric, and viscous. Both the chemical equilibrium and the nonequilibrium composition of the shock layer gas were considered. The effects of transitional range behavior were included in the analysis of high altitude entry conditions. Realistic thermophysical and radiation models were used, and results were obtained by employing the implicit finite difference technique in the shock layer and an iterative procedure for the entire shock layer precursor zone. Results obtained for a 45 degree angle hyperboloid blunt body entering Jupiter's atmosphere at zero angle of attack indicates that preheating the gas significantly increases the static pressure and temperature ahead of the shock for entry velocities exceeding 36 km/sec. The nonequilibrium radiative heating rate to the body is found to be significantly higher than the corresponding equilibrium heating. The precursor heating generally increases the radiative and convective heating of a body. That increase is slightly higher for the nonequilibrium conditions
Significance of shock and body slip conditions on Jovian entry heating
The influence of the body and shock slip conditions on the heating of a Jovian entry body is investigated. The flow in the shock layer is considered to be axisymmetric, steady, laminar, viscous, and in chemical equilibrium. Realistic thermophysical and step-function spectral models are employed and results are obtained by implicit finite-difference and iteractive procedures. The freestream conditions correspond to a typical Jovian entry trajectory point. The results indicate that the effect of the slip conditions is significant when the altitudes are higher than 225 km and that the contribution of a radiative heat-flux term in the energy equation should not be neglected at any altitude
Suppression of Conductance in a Topological Insulator Nanostep Junction
We investigate quantum transport via surface states in a nanostep junction on
the surface of a 3D topological insulator that involves two different side
surfaces. We calculate the conductance across the junction within the
scattering matrix formalism and find that as the bias voltage is increased, the
conductance of the nanostep junction is suppressed by a universal factor of 1/3
compared to the conductance of a similar planar junction based on a single
surface of a topological insulator. We also calculate and analyze the Fano
factor of the nanostep junction and predict that the Fano factor saturates at
1/5, five times smaller than for a Poisson process
Termination of Rewriting with Right-Flat Rules Modulo Permutative Theories
We present decidability results for termination of classes of term rewriting
systems modulo permutative theories. Termination and innermost termination
modulo permutative theories are shown to be decidable for term rewrite systems
(TRS) whose right-hand side terms are restricted to be shallow (variables occur
at depth at most one) and linear (each variable occurs at most once). Innermost
termination modulo permutative theories is also shown to be decidable for
shallow TRS. We first show that a shallow TRS can be transformed into a flat
(only variables and constants occur at depth one) TRS while preserving
termination and innermost termination. The decidability results are then proved
by showing that (a) for right-flat right-linear (flat) TRS, non-termination
(respectively, innermost non-termination) implies non-termination starting from
flat terms, and (b) for right-flat TRS, the existence of non-terminating
derivations starting from a given term is decidable. On the negative side, we
show PSPACE-hardness of termination and innermost termination for shallow
right-linear TRS, and undecidability of termination for flat TRS.Comment: 20 page
Effects of quarks on the formation and evolution of Z(3) walls and strings in relativistic heavy-ion collisions
We investigate the effects of explicit breaking of Z(3) symmetry due to the
presence of dynamical quarks on the formation and evolution of Z(3) walls and
associated QGP strings within Polyakov loop model. We carry out numerical
simulations of the first order quark-hadron phase transition via bubble
nucleation (which may be appropriate, for example, at finite baryon chemical
potential) in the context of relativistic heavy-ion collision experiments.
Using appropriate shifting of the order parameter in the Polyakov loop
effective potential, we calculate the bubble profiles using bounce technique,
for the true vacuum as well as for the metastable Z(3) vacua, and estimate the
associated nucleation probabilities. These different bubbles are then nucleated
and evolved and resulting formation and dynamics of Z(3) walls and QGP strings
is studied. We discuss various implications of the existence of these Z(3)
interfaces and the QGP strings, especially in view of the effects of the
explicit breaking of the Z(3) symmetry on the formation and dynamical evolution
of these objects.Comment: 17 pages, 9 figures, PDFLate
Observational study of hydrocarbons in the bright photodissociation region of Messier 8
Hydrocarbons are ubiquitous in the interstellar medium, but their formation
is still not well understood, depending on the physical environment they are
found in. M8 is host to one of the brightest HII regions and PDRs in our
galaxy. Using the APEX, and the IRAM 30 m telescopes, we performed a line
survey toward Herschel 36 (Her 36), which is the main ionizing stellar system
in M8, and an imaging survey within 1.3 1.3 pc around Her 36 of
various transitions of CH and c-CH. We used both LTE and
non-LTE methods to determine the physical conditions of the emitting gas along
with the column densities and abundances of the observed species, which we
compared with (updated) gas phase photochemical PDR models. In order to examine
the role of PAHs in the formation of small hydrocarbons and to investigate
their association with M8, we compared archival GLIMPSE 8 m and the SPIRE
250 m continuum images with the CH emission maps. We observed a
total of three rotational transitions of CH with their hyperfine
structure components and four rotational transitions of c-CH with
ortho and para symmetries toward M8. Fragmentation of PAHs seems less likely to
contribute to the formation of small hydrocarbons as the 8 m emission does
not follow the distribution of CH emission, which is more associated with
the molecular cloud. From the quantitative analysis, we obtained abundances of
10 and 10 for CH and c-CH respectively,
and volume densities of the hydrocarbon emitting gas in the range
5 10--5 10 cm. The observed column
densities of CH and c-CH are reproduced reasonably well by our
PDR models. This supports the idea that in high-UV flux PDRs, gas phase
chemistry is sufficient to explain hydrocarbon abundances.Comment: 14 pages, 10 figure
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