On the mechanism of instability in a two-layer system with limited solubility of components

A two-layer system of miscible liquids is a common model system in studies of both fundamental and applied problems in hydrodynamics that associated with stratified media. Rayleigh-Taylor instabilities or double diffusive one can lead to a disturbance in mechanical equilibrium if both or at least one of the components dissolved in each of the layers are initially unstable stratified. The situation when both components have a stable initial density distribution is believed that absolutely stable and, usually, is not considered by researchers. This paper experimentally demonstrates the possibility of developing instability in such systems and proposes a physical mechanism based on the dependence of the solubility of one of the components on the concentration of the second component. It is shown that the evolution of the density profile, the possibility of the development of instability, and the properties of the arising convective motion are determined by the initial position of the system on the parameters plane of the solubility diagram.

Signs of outflow feedback from a nearby young stellar object on the protostellar envelope around HL Tauri

Aims. HL Tau is a Class I–II protostar embedded in an infalling and rotating envelope and possibly associated with a planet forming disk, and it is co-located in a 0.1 pc molecular cloud with two nearby young stellar objects with projected distance of ~20′′–30′′ (2800–4200 au) to HL Tau. Our observations with the Atacama Large Millimeter/Submillimeter Array (ALMA) revealed two arc-like structures on a 1000 au scale connected to the disk, and their kinematics could not be explained with any conventional model of infalling and rotational motions. In this work, we investigate the nature of these arc-like structures connected to the HL Tau disk. Methods. We carried out new observations in the 13CO and C18O (3–2; 2–1) lines with the James Clerk Maxwell Telescope and the IRAM 30m telescope, and obtained the data with the 7-m array of the Atacama Compact Array (ACA). With the single-dish, ACA, and ALMA data, we analyzed the gas motions on both 0.1 pc and 1000 au scales in the HL Tau region. We constructed new kinematical models of an infalling and rotating envelope with the consideration of relative motion between HL Tau and the envelope. Results. By including the relative motion between HL Tau and its protostellar envelope, our kinematical model can explain the observed velocity features in the arc-like structures. The morphologies of the arc-like structures can also be explained with an asymmetric initial density distribution in our model envelope. In addition, our single-dish results support the scenario that HL Tau is located at the edge of a largescale (0.1 pc) expanding shell driven by the wind or outflow from XZ Tau, as suggested in the literature. The estimated expanding velocity of the shell is comparable to the relative velocity between HL Tau and its envelope in our kinematical model. These results hint that the largescale expanding motion likely impacts the protostellar envelope around HL Tau and affects its gas kinematics. We found that the mass infalling rate from the envelope onto the HL Tau disk can be decreased by a factor of two due to this impact by the largescale expanding shell.

Evolvement law of a macroscopic traffic model accounting for density-dependent relaxation time

In this paper, a modified macroscopic traffic flow model is presented. The term of the density-dependent relaxation time is introduced here. The relation between the relaxation time and the density in traffic flow is presented quantitatively. Besides, a factor R depicting varied properties of traffic flow in different traffic states is also introduced in the formulation of the model. Furthermore, the evolvement law of traffic flow with distinctly initial density distribution and boundary perturbations is emphasized.

Geostrophic adjustment in a closed basin with islands

We consider the geostrophic adjustment of a density-stratified fluid in a basin of constant depth on an $f$-plane in the context of linearized theory. For a single vertical mode, the equations are equivalent to those for a linearized shallow-water theory for a homogeneous fluid. Associated with any initial state there is a unique steady geostrophically adjusted component of the flow compatible with the initial conditions. This steady component gives the time average of the flow and is analogous to the adjusted flow in an unbounded domain without islands. The remainder of the response consists of superinertial Poincaré and subinertial Kelvin wave modes and expressions for the energy partition between the modes in arbitrary basins again follow directly from the initial conditions. The solution for an arbitrary initial density distribution released from rest in a circular domain is found in closed form. When the Rossby radius is much smaller than the basin radius, appropriate for the baroclinic modes, the interior adjusted solution is close to that of the initial state, except for small-amplitude trapped Poincaré waves, while Kelvin waves propagate around the boundaries, carrying, without change of form, the deviation of the initial height field from its average.

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

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.

The Evolution of Young Supernova Remnants

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

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.