Essays on The Economics of Aging

The increase in life expectancy in the US and the changing labor supply of older workers have raised issues about the fiscal solvency of health care and pension systems, as well as labor market stability and employment opportunities for younger workers. In light of these facts, this dissertation consists of three essays that focus on the economic causes and consequences of changes in the labor supply of older workers due to population aging. The first essay examines the effect of longevity on older Americans\u27 labor supply decisions of retirement and un-retirement. Instead of using self-rated survival probabilities as the proxy of longevity expectations, I use data from the Health and Retirement Study to predict longevity from a Gompertz survival model with a rich set of variables including parental mortality information, current health and socio-economic variables. I find that the predicted longevity fits actual longevity better than subjective survival rates. Using predicted longevity as one of the independent variables in a sequential logit model of retiring and un-retiring, I find that individuals retire and re-enter the labor market as if they knew their true potential longevity, i.e., individuals with higher predicted objective longevity retire later, and are more likely to return to the labor market after initial retirement. I further investigate the consequences of extreme mismatch between subjective survival rates and objective longevity implied by the model\u27s prediction, and I find that the misperception leads to retirees\u27 sub-optimal saving behaviors. The second essay makes an effort to explore the theoretical foundation for the mechanism through which the risk of mortality affects individuals\u27 decisions about work. I construct a life-cycle model of labor supply with health investment and heterogeneous risk of mortality. The heterogeneity in mortality risk is modeled as a frailty parameter which shifts the mortality hazard proportionally. Individuals can invest in health in order to recover from an adverse health shock and revert the high propensity of death which they were born with. I estimate and calibrate the model using data from Health and Retirement Survey. I simulate the life cycle path of labor supply for two groups of representative individuals under the same condition except for different survival curves, one in year 2000 and one projected in 2100 where life expectancy is predicted to be increased by 9 years. I find that in a more favorable survival environment, individuals would choose to work more and spend more on health. The third essay examines a natural follow-up question about the consequence of a larger labor supply of older workers: does the higher labor force participation rate of the elderly crowd out employment opportunities of younger workers? I utilize the Social Security \u27Notch\u27, a reduction in Social Security benefits for cohorts born after 1916 due to the 1977 Amendments, as an exogenous policy change to identify the effect on younger workers\u27 employment. Using data from Current Population Survey from 1972 to 1981, I do not find any significant crowding-out effect of the notch generation on younger workers age 25-39. I further investigate the variations in different occupational categories and find that changes in employment rates of younger workers vary across occupations. Last, I do not find significant suppressing effect of increasing labor supply of older workers on younger workers\u27 wage income

A recognition method of plunger wear degree of plunger pump using probability neural network

In order to increase the diagnosis efficiency of plunger wear fault, a recognition method is developed using sensitivity analysis and probability neural network. Firstly, 17 time domain characteristics of vibration signal are extracted. Then analyzed the sensitivity of characteristics to failure to select sensitive characteristics parameters. Finally, PNN method to identify the degree of plunger wear was proposed. A hydraulic pump fault simulation experiment was designed, and validated the proposed method by experimental data. The results show that the method can quickly and effectively identify the degree of plunger wear

A Novel Model of Working Set Selection for SMO Decomposition Methods

In the process of training Support Vector Machines (SVMs) by decomposition methods, working set selection is an important technique, and some exciting schemes were employed into this field. To improve working set selection, we propose a new model for working set selection in sequential minimal optimization (SMO) decomposition methods. In this model, it selects B as working set without reselection. Some properties are given by simple proof, and experiments demonstrate that the proposed method is in general faster than existing methods.Comment: 8 pages, 12 figures, it was submitted to IEEE International conference of Tools on Artificial Intelligenc

Spare support model based on gamma degradation process

Spare parts ordering is very important in the domain of system support based on condition-based maintenance. For a single-unit system with condition monitoring, a joint degradation and spare parts ordering model is established in this paper to achieve the lowest total cost rate as the objective. The degradation process of system is assumed to be followed a gamma process. A decision on optimal spare ordering time by the improved cost rate model based on the proposed degradation model is made. Finally, a case analysis is implemented to demonstrate the effectiveness of the proposed model in this paper. Analysis results show that the proposed model can reduce the cost rate effectively

Topological structure bifurcation of temperature field of deformable drop in Marangoni migration

AbstractThe unsteady processes of the Marangoni migration of deformable liquid drops are simulated numerically in a wider range of Marangoni number (up to Ma = 500) in the present work. A steady terminal state can always be reached, and the scaled terminal velocity is a monotonic function decreasing with increasing Marangoni number, which is generally in agreement with corresponding experimental data. The topological structure of flow field in the steady terminal state does not change as the Marangoni number increases, while bifurcation of the topological structure of temperature field occurs twice at two corresponding critical Marangoni numbers. A third critical value of Marangoni number also exists, beyond which the coldest point jumps from the rear stagnation to inside the drop though the topological structure of the temperature field does not change. It is found that the inner and outer thermal boundary layers may exist along the interface both inside and outside the drop if Ma > 70. But the thickness decreases with increasing Marangoni number more slowly than the prediction of potential flow at large Marangoni and Reynolds numbers