Optimal Unemployment Insurance with Variable Skill Levels

I study the consequences of heterogeneity of skills for the design of an optimal unemployment insurance, using a principal-agent set-up with a risk neutral insurer and infinitely lived risk averse agents. Agents, who are characterised by different productivities or skills, are employed by firms offering wages that depend both on the agents’ individual skill level and the quality of the worker-firm-match. Agents face the risk of losing their job and, while unemployed, are offered jobs with different match qualities. No search effort by the agent is needed to receive offers. Individual productivity declines during unemployment due to depreciation of skills and increases on the job because of learning by doing. Any insurance offered must take into account the moral hazard problem created by the fact that job offers are private information to the agent. A further complication is due to the unobservability of an agent’s productivity. I find that under an optimal contract, periods of unemployment are characterised by declining benefits. Agents are further punished for long unemployment by reducing expected future utility. A new result obtained from this approach is the observation that under an efficient contract, agents whose productivity is relatively high tend to have a shorter unemployment duration and a higher productivity growth in the future. Unemployment benefits do not only depend on an agent’s employment history, but also on the skills reported by the agent. Agents are punished for accepting jobs that do not seem to be in line with their reported skills.Unemployment Insurance, Human Capital, Adverse Selection, Moral Hazard

Allocating Time: Individuals' Technologies, Household Technology, Perfect Substitutes, and Specialization

In an efficient household if the spouses' time inputs are perfect substitutes, then spouses will “specialize" regardless of their preferences and the governance structure. That is, both spouses will not allocate time to both household production and the market sector. The perfect substitutes assumption implies that spouses' "unilateral" production functions (i.e., the household production function when only one spouse allocates time to home production) are closely related, satisfying a highly restrictive condition that I call "compatibility." I introduce the “correspondence assumption,” which postulates that the unilateral production functions in a newly formed household coincide with individuals’ production functions before they enter marriage. The correspondence assumption provides a plausible account of the genesis of household technology and simplifies its estimation. I introduce the "additivity assumption” which postulates that the household production function is the sum of the spouses' unilateral production functions and argue that additivity is implicit in much of the new home economics. Together, the correspondence and additivity assumptions imply that individuals’ technologies reveal the entire household technology. I show that perfect substitutes, additivity and concavity imply that the household production function is of the same form as the unilateral production functions, exhibits constant returns to scale, and depends on the spouses' total time inputs, measured in efficiency units.

Photoreflectance for in-situ characterization of MOCVD growth of semiconductors under micro-gravity conditions

A contactless electromodulation technique of photoreflectance (PR) was developed for in-situ monitoring of metal-organic chemical vapor deposition (MOCVD) semiconductor growth for micro-gravity applications. PR can be employed in a real MOCVD reactor including rotating substrate (approximately 500 rev/min) in flowing gases and through a diffuser plate. Measurements on GaAs and Ga(0.82)Al(0.18)As were made up to 690 C. The direct band gaps of In(x)Ga(1-x)As (x = 0.07 and 0.16) were evaluated up to 600 C. In order to address the question of real time measurement, the spectra of the direct gap of GaAs at 650 C was obtained in 30 seconds and 15 seconds seems feasible

Heavy atom quantum diffraction by scattering from surfaces

Typically one expects that when a heavy particle collides with a surface, the scattered angular distribution will follow classical mechanics. The heavy mass assures that the de Broglie wavelength of the incident particle in the direction of the propagation of the particle (the parallel direction) will be much shorter than the characteristic lattice length of the surface, thus leading to a classical description. Recent work on molecular interferometry has shown that by increasing the perpendicular coherence length, one may observe interference of very heavy species passing through a grating. Here we show, using quantum mechanical simulations, that the same effect will lead to quantum diffraction of heavy particles colliding with a surface. We find that the effect is robust with respect to the incident energy, the angle of incidence and the mass of the particle. It may also be used to verify the quantum nature of the surface and its fluctuations at very low temperatures.Comment: 9 pages, 3 figure

Nonexponential Relaxations in a Two-Dimensional Electron System in Silicon

The relaxations of conductivity have been studied in a strongly disordered two-dimensional (2D) electron system in Si after excitation far from equilibrium by a rapid change of carrier density n_s at low temperatures T. The dramatic and precise dependence of the relaxations on n_s and T strongly suggests (a) the transition to a glassy phase as T->0, and (b) the Coulomb interactions between 2D electrons play a dominant role in the observed out-of-equilibrium dynamics.Comment: 5 pages, 5 figure

Why Are Power Couples Increasingly Concentrated in Large Metropolitan Areas

Using census data, Costa and Kahn (QJE, 2000) find that power couples - couples in which both spouses have college degrees - are increasingly likely to be located in the largest metropolitan areas. One explanation for this trend is that college educated couples are more likely to face a co-location problem - the desire to satisfy the career aspirations of both spouses - and therefore are more attracted to large labor markets than are other couples. An alternative explanation is that all college educated individuals, married and unmarried, are attracted to the amenities and high returns to education found in large cities and that as a result, the formation of power couples through marriage of educated singles and additional education is more likely to occur in larger than smaller metropolitan areas. Using the Panel Study of Income Dynamics (PSID), we analyze the dynamic patterns of migration, marriage, divorce and education in relation to city size and find that power couples are not more likely to migrate to the largest cities than part-power couples or power singles. Instead, the location trends are better explained by the higher rate of power couple formation in larger metropolitan areas. Regression analysis suggests that it is only the education of the husband and not the joint education profile of the couple that affects the propensity to migrate to large metropolitan areas.