scholarly journals The Ionization and Expansion of a Globule of Interstellar Gas overun by a Weak R Type Ionization Front

1977 ◽  
Vol 32 (7) ◽  
pp. 692-696
Author(s):  
J. S. Berry
Keyword(s):  
Density Distribution ◽  
Similarity Solution ◽  
Spherical Symmetry ◽  
Initial Density ◽  
Neutral Hydrogen ◽  
Ionization Front ◽  
Interstellar Gas ◽  
Ionized Gas ◽  
Initial Density Distribution

Abstract The flow of the ionized gas behind a contracting ionization front is investigated for spherical symmetry. A similarity solution is given when the initial density distribution in the neutral hydrogen is ω0/rα- where r is the distance from the centre of contraction.

Ionization fronts in interstellar gas and the expansion of HII regions

1961 ◽  
Vol 253 (1028) ◽  
pp. 277-300 ◽  
Keyword(s):  
Equations Of Motion ◽  
Initial Density ◽  
Neutral Hydrogen ◽  
Similarity Solutions ◽  
Ionization Front ◽  
H Ii Regions ◽  
Interstellar Gas ◽  
Ionized Gas ◽  
Ionization Fronts ◽  
H Ii Region

The gas dynamical effects of an expanding nearly fully ionized hydrogen region (H II region), which is associated with the formation of O and B stars, are investigated. The radiation from the hot star is absorbed by the surrounding interstellar gas (mainly neutral hydrogen) and leads to its ionization. Previous analyses have disregarded the internal motions set up in expanding H II regions. Similarity solutions of the equations of motion are presented for spherical and cylindrical problems, thus enabling the effects of groups of stars as well as individual stars to be discussed. For similarity to be applicable the initial density variations of the undisturbed neutral gas have to be like 1/ r ® in the spherical case and like 1/ r in the cylindrical case. This does not, however, limit their use in describing the general picture of events for any other given density distribution. Recombination of the ions and electrons and subsequent re-ionization by radiation within the H II region is allowed for; cooling processes such as that due to the excitation of O<super>+</super> ions are also taken into account. It is shown that the temperature of the ionized gas in the H II region is approximately uniform even though the region as a whole is expanding. Rates of expansion are calculated and it is also determined whether a shock propagates ahead of the ionized gas. In particular for rates of expansion less than about 20 km/s a shock wave occurs ahead, but for speeds greater than about 20 km/s, which would occur in the initial motion, the rate of expansion of the ionized gas is too great and an ‘isothermal’ shock occurs within the H II region. The boundary between the ionized and neutral gases can be regarded as a discontinuity and is termed an ionization front. The present paper is concerned with the propagation of such fronts and accompanying shocks; a companion paper by W. I. Axford investigates the structures of ‘isothermal shock’ and ionization fronts. The lack of uniqueness, which occurs in the present paper, is removed when the results are combined with Axford’s work.

EFFECTS OF INITIAL INHOMOGENEOUS DENSITY DISTRIBUTION AND VOID SHAPE ON POWDER FORGING OF POROUS METAL

2013 ◽  
Vol 27 (19) ◽  
pp. 1341008
Author(s):  
TAIQING DENG ◽  
LIANXI HU ◽  
YU SUN ◽  
XIAOYA LIU
Keyword(s):  
Density Distribution ◽  
Initial Density ◽  
Porous Metal ◽  
Major Axis ◽  
Average Density ◽  
Semi Major Axis ◽  
Punch Force ◽  
Inhomogeneous Density ◽  
Void Shape ◽  
Initial Density Distribution

The deformation behavior during axisymmetric upsetting of sintered metals has been studied based on the finite-element method. The investigation on the effects of the initial density distribution, void shape and die friction on the density distribution and punch force during deformation have been conducted. It was found that under low-friction conditions, the initial density distribution affects the deformation geometry and the density distribution. However, the effect of the initial density distribution was found to be negligible under high-friction conditions. The initial density distribution did not affect the punch force or the average density, regardless of the friction conditions. When the force is perpendicular to semi-major axis of elliptical void, it is not only good for densification but also decrease the punch force in forging of porous metal.

IV.—Expansion of a Finite One-dimensional Gas Cloud into a Vacuum

1953 ◽  
Vol 64 (1) ◽  
pp. 57-70
Author(s):  
A. G. Mackie
Keyword(s):  
Density Distribution ◽  
Analytical Solutions ◽  
Initial Density ◽  
Initial Distribution ◽  
One Dimensional ◽  
Gas Streams ◽  
Subsequent Motion ◽  
Gas Cloud ◽  
Initial Density Distribution ◽  
Stationary Period

SynopsisAn investigation is made of the motion of a one-dimensional finite gas cloud which is initially at rest and is allowed to expand into a vacuum in both directions. The density of the gas at rest is assumed to rise steadily and continuously from zero at the boundaries to a maximum in the interior of the cloud.If the subsequent motion is continuous, it is completely specified by analytical solutions in seven different regions of the x-t plane joined together along characteristics. The motion of one of the boundaries is discussed, and conditions found for it to have (i) an initial stationary period or (ii) a final constant velocity of advance into the vacuum. The gas streams in both directions from a dividing point at zero velocity. This point ultimately tends to the mid-point of the initial distribution.The possible breakdown of the continuity of the motion is discussed, and a condition on the initial density distribution found for shock-free flow to be maintained.

Ionization front in interstellar gas: The structure of ionization fronts

1961 ◽  
Vol 253 (1029) ◽  
pp. 301-333 ◽  
Keyword(s):  
Cylindrical Symmetry ◽  
Ionization Front ◽  
Complete Analysis ◽  
Interstellar Gas ◽  
Ionized Gas ◽  
Important Condition ◽  
Ionization Fronts ◽  
Gas Dynamic ◽  
Cooling Effects ◽  
Stagnation Enthalpy

A complete analysis of the structures of all types of ionization front is given, together with computed examples. It is shown that the solutions given by Goldsworthy for the propagation of ionization fronts, considered as discontinuities, can be made unique, and the unique solutions are given for the case of cylindrical symmetry. Ionization fronts of all types are shown to be possible, depending on the density of the ionized gas and the spectral type of the radiation. In particular strong D -type and weak R -type ionization fronts (corresponding to strong deflagrations and weak detonations, respectively, in combustion theory) prove to be of importance. The existence of these discontinuities conflicts with the Chapman-Jouguet hypothesis and the reasons for this behaviour are examined in detail. It is concluded that the most important condition for waves of this type to occur is that strong cooling effects should be present, which allow the stagnation enthalpy of the flow to have a maximum before decreasing to an equilibrium value at the rear of the wave. It is suggested that this may be of significance in the theory of other gas-dynamic discontinuities, and in determining the validity of the Chapman—Jouguet hypothesis in general.

The normal motion of a shock wave through a non-uniform one-dimensional medium

1955 ◽  
Vol 232 (1190) ◽  
pp. 350-370 ◽  
Keyword(s):  
Shock Wave ◽  
Density Distribution ◽  
Contact Discontinuity ◽  
Initial Density ◽  
Incident Shock ◽  
Shock Strength ◽  
Total Strength ◽  
Reflected Wave ◽  
Uniform Medium ◽  
Initial Density Distribution

The non-uniform medium is regarded as a succession of small-density discontinuities separated by uniform regions. Consideration of the interaction of a shock wave with a weak contact discontinuity gives a first-order relationship between change in shock strength and change in density across the discontinuity, which is integrated to give the shock strength as a function of the initial density of the non-uniform medium in closed form. Due to the passage of the shock, a wave is reflected back through the non-uniform medium, generating in turn a doubly reflected wave which eventually catches up the shock. A complete description of the flow as modified by the first reflected wave is obtained. The modifications to the flow caused by the doubly reflected wave are more difficult to formulate, and a complete description of the flow so modified is not given. The extra difficulty is partly due to the dependence of the doubly reflected wave on the initial density distribution, whereas the motion of the incident shock, and the flow behind it as modified only by the first reflected wave, are found to have the useful property that they are independent of the particular density-distance distribution being considered. Calculations of the total strength of the doubly reflected wave, and the strength of the incident shock when this wave has fully merged with it, have been made for a particular density distribution. A comparison of this calculated strength with the strength of the shock transmitted, after the interaction of a shock wave and a contact discontinuity, suggests that a description of the flow which takes account only of the single and double reflexions is satisfactory, even if the initial density distribution varies considerably.

scholarly journals The Evolution of Young Supernova Remnants

1983 ◽  
Vol 101 ◽  
pp. 119-124
Author(s):  
A. C. Fabian ◽  
W. Brinkmann ◽  
G. C. Stewart
Keyword(s):  
Density Distribution ◽  
Stellar Wind ◽  
Supernova Remnants ◽  
Initial Conditions ◽  
Numerical Models ◽  
Variable Mass ◽  
Initial Density ◽  
X Ray ◽  
Cassiopeia A ◽  
Initial Density Distribution

Einstein X-ray observations of the young supernova remnants Cassiopeia A (Murray et al. 1980) and Tycho (Seward, Gorenstein and Tucker 1982) indicate that the swept-up mass does not much exceed that of the observed ejecta. The initial density distribution of the ejecta and surrounding material is then important in determining the X-ray structure and evolution. Some aspects of this behaviour have been dealt with in previous numerical (e.g. Gull 1973; Itoh 1977; Jones, Smith and Straka 1981) and analytical (e.g. Chevalier 1982a,b) studies. We present here results obtained from numerical models covering a wider range of initial conditions. In particular, we consider the effect of a constant stellar wind from the progenitor star on the expansion of the remnant. We have previously suggested that variable mass loss from SN1006 may explain its warm filled interior (Fabian, Stewart and Brinkmann 1982).

Computed Dynamic Compaction of a Two-Layered Copper Powder Medium

1979 ◽  
Vol 101 (2) ◽  
pp. 122-128
Author(s):  
Yukio Sano ◽  
Kiyohiro Miyagi
Keyword(s):  
Density Distribution ◽  
Layered Medium ◽  
Initial Density ◽  
Dynamic Compaction ◽  
Volume Distribution ◽  
Green Density ◽  
Compaction Process ◽  
Density Distributions ◽  
Powder Medium ◽  
Initial Density Distribution

In the paper presented a dynamic compaction of a two-layered powder medium is analyzed. A two-layered medium is used because it is the simplest form of layered medium available. The layers are differentiated not in terms of different powdered materials but rather a difference in terms of initial-density (initial specific volume) distribution, that is a higher initial density distribution and a lower initial density distribution. Again for these initial density distributions, two forms of arrangement can be considered; for the first situation, the layer to be impacted has a lower initial density distribution, while for the second situation the arrangement is reversed. The objective of this paper, therefore, is to examine the effect that the initial density sequence has on the compaction process and on the green density of a layered powder medium, especially in terms of shock wave and elastic wave influence.

scholarly journals Variable-density buoyancy-driven turbulence with asymmetric initial density distribution

2020 ◽  
Vol 406 ◽  
pp. 132444 ◽  
Author(s):  
Denis Aslangil ◽  
Daniel Livescu ◽  
Arindam Banerjee
Keyword(s):  
Density Distribution ◽  
Initial Density ◽  
Variable Density ◽  
Initial Density Distribution

Estimation of the initial density distribution in plasma–metal liners

2016 ◽  
Vol 61 (5) ◽  
pp. 676-682 ◽  
Author(s):  
A. G. Rousskikh ◽  
A. S. Zhigalin ◽  
V. I. Oreshkin
Keyword(s):  
Density Distribution ◽  
Initial Density ◽  
Initial Density Distribution
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