Orbital migration of low-mass planets in evolutionary radiative models: Avoiding catastrophic infall

Outward migration of low-mass planets has recently been shown to be a possibility in non-barotropic disks. We examine the consequences of this result in evolutionary models of protoplanetary disks. Planet migration occurs towards equilibrium radii with zero torque. These radii themselves migrate inwards because of viscous accretion and photoevaporation. We show that as the surface density and temperature fall, the planet orbital migration and disk depletion timescales eventually become comparable, with the precise timing depending on the mass of the planet. When this occurs, the planet decouples from the equilibrium radius. At this time, however, the gas surface density is already too low to drive substantial further migration. A higher mass planet, of 10 Earth masses, can open a gap during the late evolution of the disk, and stops migrating. Low mass planets, with 1 or 0.1 Earth masses, released beyond 1 AU in our models, avoid migrating into the star. Our results provide support for the reduced migration rates adopted in recent planet population synthesis models.Comment: 6 pages, 4 figures. Accepted by ApJ. In press

How has internal migration in Albania affected the receipt of transfers from family and friends?

Social networks of family and friends are very important in providing economic and social support to households. The massive internal migration flows towards the big cities in the transition countries like Albania can seriously affect such networks, and influence the support received. Previous migration studies have analysed mostly the transfers between the migrant and the family left behind. This study analyses households that migrate together to the peripheries of Tirana (Albania) after the fall of the communist regime. The frequencies of transfers received before and after migration are used to test the change in the composition of transfers and the substitution of family members by friends after migrating. The empirical analysis shows that households receive fewer transfers after migration, but financial transfers increase. Friends become increasingly more important after migration, substituting for transfers from siblings and more distant family relatives.kinship networks; internal migration; Albania; inter-household transfers

The Brain Drain and the World Distribution of Income and Population Growth

Over the last two decades immigration policies in OECD economies have become increasingly selective and the rate of skilled migration from low income economies has risen markedly. This paper analyzes the theoretical implications of this shift in migration patterns for the growth and distribution of world income and population using a model with endogenous education, fertility and migration decisions in both the sending and receiving economies. It shows that Brain Drain migration may cause fertility to fall and human capital accumulation to increase in both the sending and receiving economies. It also shows that the world economy may converge to a special kind of core-periphery equilibrium where increasing inequality between countries is fueled by Brain Drain migration but where, nonetheless, the welfare of agents in both the core and the periphery is increased. Thus Brain Drain migration may increase inequality between countries at the same time as reducing world poverty and increasing world growth.Migration, Growth

A control function approach to estimating dynamic probit models with endogenous regressors, with an application to the study of poverty persistence in China

This paper proposes a parametric approach to estimating a dynamic binary response panel data model that allows for endogenous contemporaneous regressors. This approach is of particular value for settings in which one wants to estimate the effects of an endogenous treatment on a binary outcome. The model is next used to examine the impact of rural-urban migration on the likelihood that households in rural China fall below the poverty line. In this application, it is shown that migration is important for reducing the likelihood that poor households remain in poverty and that non-poor households fall into poverty. Furthermore, it is demonstrated that failure to control for unobserved heterogeneity would lead the researcher to underestimate the impact of migrant labor markets on reducing the probability of falling into poverty.Rural Poverty Reduction,Population Policies,Achieving Shared Growth,Debt Markets,Regional Economic Development

Migration, trade, and foreign investment in Mexico

Part of the rationale for the North American Free Trade Agreement (NAFTA) was that it would increase trade and foreign direct investment (FDI) flows, creating jobs and reducing migration to the United States. Since poor data on illegal flows to the United States make direct measurement difficult, Aroca and Maloney instead evaluate the mechanism behind these predictions using data on migration within Mexico where the census data permit careful analysis. They offer the first specifications for migration within Mexico, incorporating measures of cost of living, amenities, and networks. Contrary to much of the literature, labor market variables enter very significantly and as predicted once the authors control for possible credit constraint effects. Greater exposure to FDI and trade deters out-migration with the effects working partly through the labor market. Finally, the authors generate some tentative inferences about the impact on increased FDI on Mexico-U.S. migration. On average, a doubling of FDI inflows leads to a 1.5-2 percent fall in migration.Economic Theory&Research,Health Monitoring&Evaluation,Environmental Economics&Policies,Banks&Banking Reform,Municipal Financial Management

The migration of fluid droplets and their interactions in a thermal gradient

When materials are processed in free fall, buoyant forces will be substantially reduced. Thus, the buoyant migration of droplets and bubbles which normally occurs on earth is expected to be overshadowed by migration due to other mechanisms in space processing. In particular, capillary forces on droplets due to the variation of interfacial tension around their periphery will play a significant role in governing their motion in space. While such interfacial tension gradients can be caused by thermal, compositional, and/or electrical gradients in the continuous phase, thermal gradients are convenient to use in controlled experimentation. On earth, due to interference from buoyant effects, it is difficult to study thermocapillary migration in sufficient detail. Also, the effects of a thermal gradient on the interactions among droplets are hard to study on Earth. Thus, an orbital facility for conducting experiments on the migration and interactions of fluid droplets in a continuous phase due to the action of a thermal gradient appears attractive

Endogenous migration in a two-country model with labor market frictions

We present a dynamic North-South model with search frictions and endogenous labor migration to study the long-run implications of labor factor mobility on labor market conditions and welfare. In the model, the high-TFP country (North) acts as the destination country for migration, while the low-TFP country (South) acts as the origin country. We prove that there always exists a unique steady-state equilibrium for the world economy, and find that a permanent increase in migration effort causes per capita income to rise in North and to fall in South. However, our simulations also show the existence of a job displacement effect in the host country that makes domestic employment fall in the long-run. In an extension of the baseline model, we test the long-run effects of a pro-employment protectionist policy of the destination country consisting in imposing a distortionary tax on the domestic firms hiring migrant workers. Our analysis shows that a positive tax rate on foreign employment can increase natives welfare, but only at the expense of losses in national production and employment. These results are robust across different degrees of substitutability between migrant and native workers

Rural to Urban Migration and Changes in Cardiovascular risk Factors in Tanzania: A Prospective Cohort Study.

High levels of rural to urban migration are a feature of most African countries. Our aim was to investigate changes, and their determinants, in cardiovascular risk factors on rural to urban migration in Tanzania. Men and women (15 to 59 years) intending to migrate from Morogoro rural region to Dar es Salaam for at least 6 months were identified. Measurements were made at least one week but no more than one month prior to migration, and 1 to 3 monthly after migration. Outcome measures included body mass index, blood pressure, fasting lipids, and self reported physical activity and diet. One hundred and three men, 106 women, mean age 29 years, were recruited and 132 (63.2%) followed to 12 months. All the figures presented here refer to the difference between baseline and 12 months in these 132 individuals. Vigorous physical activity declined (79.4% to 26.5% in men, 37.8% to 15.6% in women, p < 0.001), and weight increased (2.30 kg men, 2.35 kg women, p < 0.001). Intake of red meat increased, but so did the intake of fresh fruit and vegetables. HDL cholesterol increased in men and women (0.24, 0.25 mmoll-1 respectively, p < 0.001); and in men, not women, total cholesterol increased (0.42 mmoll-1, p = 0.01), and triglycerides fell (0.31 mmoll-1, p = 0.034). Blood pressure appeared to fall in both men and women. For example, in men systolic blood pressure fell by 5.4 mmHg, p = 0.007, and in women by 8.6 mmHg, p = 0.001. The lower level of physical activity and increasing weight will increase the risk of diabetes and cardiovascular disease. However, changes in diet were mixed, and may have contributed to mixed changes in lipid profiles and a lack of rise in blood pressure. A better understanding of the changes occurring on rural to urban migration is needed to guide preventive measures