Coresidence with Parents and a Wife's Decision to Work in Japan

The purpose of this paper is to analyze the factors that would affect the married couple's decision to coreside with their parents and a wife's decision to work in Japan, explicitly considering the simultaneous structure of these two decisions. Unlike preceding studies, we distinguish coresidence with the husband's parents and that with the wife's parents. Our empirical analysis based on the micro-data shows that the positive impact of coresidence with parents on the wife's labor participation tends to be underestimated, unless simultaneous decisions are taken into account. It is also found that the couple's decision to coreside with their parents is influenced by socio-economic and demographic factors such as the couple's educational attainments as well as the family relations.coresidence, Japan, a wife's labor participation

Dynamical Expansion of H II Regions from Ultracompact to Compact Sizes in Turbulent, Self-Gravitating Molecular Clouds

The nature of ultracompact H II regions (UCHRs) remains poorly determined. In particular, they are about an order of magnitude more common than would be expected if they formed around young massive stars and lasted for one dynamical time, around 10^4 yr. We here perform three-dimensional numerical simulations of the expansion of an H II region into self-gravitating, radiatively cooled gas, both with and without supersonic turbulent flows. In the laminar case, we find that H II region expansion in a collapsing core produces nearly spherical shells, even if the ionizing source is off-center in the core. This agrees with analytic models of blast waves in power-law media. In the turbulent case, we find that the H II region does not disrupt the central collapsing region, but rather sweeps up a shell of gas in which further collapse occurs. Although this does not constitute triggering, as the swept-up gas would eventually have collapsed anyway, it does expose the collapsing regions to ionizing radiation. We suggest that these regions of secondary collapse, which will not all themselves form massive stars, may form the bulk of observed UCHRs. As the larger shell will take over 10^5 years to complete its evolution, this could solve the timescale problem. Our suggestion is supported by the ubiquitous observation of more diffuse emission surrounding UCHRs.Comment: accepted to ApJ, 40 pages, 13 b/w figures, changes from v1 include analytic prediction of radio luminosity, better description of code testing, and many minor changes also in response to refere

On Hydrodynamic Motions in Dead Zones

We investigate fluid motions near the midplane of vertically stratified accretion disks with highly resistive midplanes. In such disks, the magnetorotational instability drives turbulence in thin layers surrounding a resistive, stable dead zone. The turbulent layers in turn drive motions in the dead zone. We examine the properties of these motions using three-dimensional, stratified, local, shearing-box, non-ideal, magnetohydrodynamical simulations. Although the turbulence in the active zones provides a source of vorticity to the midplane, no evidence for coherent vortices is found in our simulations. It appears that this is because of strong vertical oscillations in the dead zone. By analyzing time series of azimuthally-averaged flow quantities, we identify an axisymmetric wave mode particular to models with dead zones. This mode is reduced in amplitude, but not suppressed entirely, by changing the equation of state from isothermal to ideal. These waves are too low-frequency to affect sedimentation of dust to the midplane, but may have significance for the gravitational stability of the resulting midplane dust layers.Comment: 36 pages, 19 figures. ApJ accepte

Magnetorotational turbulence transports angular momentum in stratified disks with low magnetic Prandtl number but magnetic Reynolds number above a critical value

The magnetorotational instability (MRI) may dominate outward transport of angular momentum in accretion disks, allowing material to fall onto the central object. Previous work has established that the MRI can drive a mean-field dynamo, possibly leading to a self-sustaining accretion system. Recently, however, simulations of the scaling of the angular momentum transport parameter \alphaSS with the magnetic Prandtl number \Prandtl have cast doubt on the ability of the MRI to transport astrophysically relevant amounts of angular momentum in real disk systems. Here, we use simulations including explicit physical viscosity and resistivity to show that when vertical stratification is included, mean field dynamo action operates, driving the system to a configuration in which the magnetic field is not fully helical. This relaxes the constraints on the generated field provided by magnetic helicity conservation, allowing the generation of a mean field on timescales independent of the resistivity. Our models demonstrate the existence of a critical magnetic Reynolds number \Rmagc, below which transport becomes strongly \Prandtl-dependent and chaotic, but above which the transport is steady and \Prandtl-independent. Prior simulations showing \Prandtl-dependence had \Rmag < \Rmagc. We conjecture that this steady regime is possible because the mean field dynamo is not helicity-limited and thus does not depend on the details of the helicity ejection process. Scaling to realistic astrophysical parameters suggests that disks around both protostars and stellar mass black holes have \Rmag >> \Rmagc. Thus, we suggest that the strong \Prandtl dependence seen in recent simulations does not occur in real systems.Comment: 17 pages, 9 figures. as accepted to Ap