On-the-job search in urban areas

This study develops an on-the-job search model involving spatial structure. In this model, workers are either employed and commuting frequently to a central business district (CBD) or unemployed and commuting less frequently to the CBD to search for a job. When an unemployed worker succeeds in off-the-job search, the quality of the job match is determined stochastically: a good match yields high-productivity whereas a bad match yields low-productivity. Although a high-productivity worker does not search for a new job, a lowproductivity worker decides whether to conduct an on-the-job search, which would require additional commuting to the CBD. Analysis of this model demonstrates that in equilibrium, the relocation path of workers corresponds to their career path, while welfare analysis demonstrates that such a spatial structure distorts firmsf decision regarding the posting of vacancies.City structure; On-the-job search; Unemployment; Efficiency; Relocation and career paths;

Fuel Tracer Laser-induced Fluorescence for Droplet Liquid-Vapor Visualization

In order to understand the fuel droplet vaporization process in engine cycles, measurements of the local concentration of fuel vapor in high temperature and pressure environments are required. To achieve this, planar laser-induced fluorescence (PLIF) of well-characterized tracer molecules are used to track the local fuel vapor concentration. For many tracer molecules of interest, there is a strong quenching effect of local oxygen. This work aims to control and determine the quenching environment to allow quantitative measurements. For this purpose, a fluid system is designed to vary the amount of dissolved oxygen within the fuel tracer using a pressurized storage vessel. To verify the removal of dissolved oxygen from the tracer molecules, laser-induced measurements of the phosphorescence lifetime of the \u27oxygen-free\u27 fuel vapor in nitrogen bath gas is made using the fourth harmonic output of an Nd:YAG laser. A fast-time-gated ICCD camera is used to take images and determine both the fluorescence and phosphorescence lifetimes with this laser excitation. Ultimately, these techniques will allow measurements of fuel concentration at high temperature and pressure conditions during engine cycles through better understanding of the purge requirements for quenching-free measurements

Microscopic theory of spin Seebeck effect in antiferromagnets

We develop a microscopic theory for the spin Seebeck effect (SSE) in N\'eel and canted phases of antiferromagnetic insulators. We calculate the DC spin current tunneling from the antiferromagnet to an attached metal, incorporating the spin-wave theory and the non-equilibrium Green's function approach. Our result shows a sign change of the spin current at the spin-flop phase transition between N\'eel and canted phases, which is in agreement with a recent experiment for the SSE of $\rm Cr_2O_3$ in a semi-quantitative level. The sign change can be interpreted from the argument based on the density of states of up- and down-spin magnons, which is related to the polarized-neutron scattering spectra. The theory also demonstrates that the spin current in the N\'eel phase is governed by the magnon correlation, while that in the canted phase consists of two parts: Contributions from not only the magnon dynamics but also the static transverse magnetization. This result leads to a prediction that at sufficiently low temperatures, the spin current non-monotonically changes as a function of magnetic field in the canted phase. Towards a more unified understanding of the SSE in antiferromagnets, we further discuss some missing links of theories of SSE: Interface properties, effects of the transverse spin moment in the canted phase, the spin-orbit coupling in the metal, etc. Finally, we compare the SSE of antiferromagnets with those of different magnetic phases such as ferromagnets, ferrimagnets, an one-dimensional spin liquid, a spin-nematic liquid, and a spin-Peierls (dimerized) phase.Comment: 25 pages, 14 figure

A BOUNDING ALGORITHM FOR SELECTIVE GRAPH COLORING PROBLEM (Development of Mathematical Optimization : Modeling and Algorithms)

This note addresses the selective graph coloring problem, which is a generalization of the well-known vertex coloring problem. Given an undirected graph together with a partition of its vertex set, it is to find a subset of the vertex set which shares exactly one vertex with each component of the partition so that the chromatic number of the subgraph induced by the subset is minimum. In this note, we present a new column generation algorithm for a linear programming relaxation problem of the selective graph coloring

Analyzing the impact of labor market integration

We develop a competitive search model involving multiple regions, geographically mobile workers, and moving costs. Equilibrium mobility patterns are analyzed and characterized, indicating that shocks to a particular region, such as a productivity shock, can propagate to other regions through workers' mobility. Moreover, equilibrium mobility patterns are not efficient due to the existence of moving costs, implying that they affect social welfare not only because they are costs but also because they distort equilibrium allocation. By calibrating our framework to Japanese regional data, we demonstrate that the impacts of eliminating migration costs are comparable to those of a 30% productivity increase