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Countries with strict immigration policies often resort to deportation measures to reduce their stocks of illegal immigrants. Many of their undocumented foreign workers, however, are not deported but rather choose to return home voluntarily. This paper studies the optimizing behavior of undocumented immigrants who continuously face the risk of deportation, modeled by a stochastic process, and must decide how long to remain in the host country. It is found that the presence of uncertainty with respect to the length of stay abroad unambiguously reduces the desired migration duration and may trigger a voluntary return when a permanent stay would otherwise be optimal. Voluntary return is motivated by both economic and psychological factors. Calibration of the model to match the evidence on undocumented Thai migrants in Japan suggests that the psychological impact of being abroad as an illegal alien may be equivalent to as large as a 68% cut in the consumption rate at the point of return.

A magnetic fluid (MF) changes its surface shape in the magnetic field of a current-carrying wire while the current is changing. In the present paper, we propose to study a MF bridge which can open or close the channel formed by two cones and a cylinder by imposing the magnetic field of a wire. Numerical modelling of the bridge behavior for different values of MF volumes and currents in the wire is done for two cases: when the MF wets and does not wet surrounding solid boundaries. It is shown that the presence of limiting cones allows the MF to sustain the pressure drop which is much higher in case of non-wetting than in case of wetting. In case of wetting, the MF cannot sustain any pressure drop at low currents, but in case of non-wetting, the MF can do it even at zero current. It is found that in case of non-wetting, spasmodic and hysteresis phenomena are possible for some values of MF volumes and currents in the wire. The use of a MF in valves, dispensers and pumps is one of possible actuation methods.

Risks to human health stemming from polluted air, water, and soil are substantial, especially in the rapidly growing economies. The present paper develops a theoretical framework to study an endogenously growing economy which is subject to pollution-induced health shocks with the health status being an argument of the welfare function. Pollution, arising as a negative externality from production, adversely and randomly affects the regeneration ability of a human body leading to a decline in the overall health status of the population. We include two types of uncertainty surrounding the health status: continuous small-scale fluctuations, driven by the Wiener process, and large-scale shocks or epidemics, driven by the Poisson process. We derive closed-form analytical solutions for the optimal abatement policy and the growth rate of consumption. Devoting a constant fraction of output to emissions abatement delivers the first-best allocation. This fraction is an increasing function of total factor productivity, polluting intensity of production, and damage intensity of both continuous and jump-type shocks. A higher frequency of jumps also calls for more vigorous abatement policies. By contrast, the optimal growth rate of the economy is decreasing in the frequency and intensity of shocks and in the polluting intensity of output. The efficiency of abatement technology has, in general, an ambiguous bearing on both the growth rate and on the abatement share due to the opposing forces of the direct and indirect effects.

The present study examines the problem facing a resource-importing economy seeking to achieve energy independence by developing a renewable substitute. The invention of the substitute is assumed to follow a stochastic process that can be influenced by investment in energy research and development. I analyze the optimal investment strategy under alternative assumptions with respect to the economy's access to international financial markets, the terms on which credit is available, and the country's degree of dependence on resource imports. It is found that, in general, having access to capital markets does not necessarily lead to a higher investment rate. However, in the empirically relevant range of elasticity of intertemporal consumption substitution, the economy with access to credit invests more than under financial autarky. A higher degree of dependence on resource imports implies a lower optimal investment. Arrival of the substitute does not necessarily cause an immediate improvement in the net foreign asset position but may in fact cause its further deterioration.

Savings of guest workers as well as of undocumented migrants represent important inflows of foreign exchange for some developing countries. This paper compares the saving behavior of these two types of migrants, assuming that the former are authorized to work abroad for a specific period of time, while the latter can stay until apprehended and deported by the immigration authorities. Due to the risk of deportation, the saving rate of an illegal immigrant is found to be initially above that of a documented migrant. This precautionary saving phenomenon is, however, short-lived. A key finding of the paper is that the total repatriated assets of an illegal migrant are always lower than those of a documented worker, provided that their duration of stay abroad is identical. This is because the undocumented migrant's saving rate falls over time as her expected lifetime earnings are adjusted upwards every day that she avoids apprehension.

What determines whether a temporary migrant chooses to go abroad as a documented worker or as an illegal alien? We address the question from a theoretical perspective by focusing on how immigration policies, aimed at both documented and undocumented foreign workers, influence the choice between the two modes of migration. Calibrating our model to the specific case of temporary emigration from Thailand, we provide estimates of the relative policy effectiveness. The deportation rate facing undocumented aliens is shown to be the most potent instrument, while some of the measures directed at documented contract workers are found to be more effective in influencing the choice of emigration mode than border controls and employer sanctions aimed at illegal immigrants.

The paper derives general rules for equitable burden sharing in international climate policy. The focus is on a new social climate contract between developed and less developed countries (LDCs) which preserves competitiveness of the former and the “right to development” of the latter. We formally derive conditions under which an LDC keeps the “right to development” but voluntarily agrees to participate in stringent international climate policy. Two types of policies are analyzed, one with a predefined transfer and the other with a transfer that is tied to emissions-control efforts. We show that offering only one or the other option is inefficient. Chances for a comprehensive agreement are higher when a menu of policy options is available. The number and diversity of LDCs willing to join a global climate treaty is higher when a variety of policy alternatives is available.

We consider a heavy, incompressible, homogenous, isothermal magnetic fluid between two coaxial cylinders in case of wetting. There is a current-carrying straight wire on the axis of these cylinders. The magnetic fluid is immersed in a non-magnetic liquid with the same density (the case of hydroimponderability). We apply the Langevin law to describe a magnetic fluid magnetization. Using the general analytical solution for any axially symmetric shape of the magnetic fluid free surface in any axisymmetric magnetic field, we investigate the break-up and the rebuilding of the magnetic fluid bridge in case of wetting.

Climate economics has been criticized for ignoring uncertainty, catastrophic changes, and tipping points (Stern 2016). The present paper addresses these issues. We consider multiple climate shocks which are recurring, random, uninsurable, and potentially large. The associated damages and the hazard rate are endogenously driven by the stock of greenhouse gases. We provide closed-form solutions for the optimal climate policy and the growth rate of the economy. The optimal path is characterized by a constant growth rate of consumption and of the capital stock until a shock arrives, triggering a downward jump in both variables. The mitigation policy consists of a simple and intuitive rule which requires spending a constant fraction of output on emissions abatement. In a quantitative assessment we show that under favorable conditions the abatement expenditure represents 0.5% of output, equivalent to $37 per ton carbon. Under less favorable conditions with respect to abatement technology and damages, coupled with a relative risk aversion which exceeds unity, the abatement propensity increases to 2.9%, equivalent to $212 per ton carbon, and it jumps to a striking 10% in the pessimistic scenario involving severe shocks and a possible crossing of a tipping point.

The paper derives general rules for equitable burden sharing in international climate policy. The focus is on a new social climate contract between developed and less developed countries (LDCs) which preserves competitiveness of the former and the \"right to development\" of the latter. We formally derive conditions under which an LDC keeps the \"right to development\" but voluntarily agrees to participate in stringent international climate policy. Two types of policies are analyzed, one with a predefined transfer and the other with a transfer that is tied to emissions-control efforts. We show that offering only one or the other option is inefficient. Chances for a comprehensive agreement are higher when a menu of policy options is available. The number and diversity of LDCs willing to join a global climate treaty is higher when a variety of policy alternatives is available.