Linearization of Time-Varying Nonlinear Systems Using A Modified Linear Iterative Method

The linearization of nonlinear systems is an important digital enhancement technique. In this paper, a real-time capable post- and pre-linearization method for the widely applicable time-varying discrete-time Volterra series is presented. To this end, an alternative view on the Volterra series is established, which enables the utilization of certain modified linear iterative methods for linearization. For one particular linear iterative method, the Richardson iteration, the corresponding post- and pre-linearizers are discussed in detail. It is motivated that the resulting algorithm can be regarded as a generalization of some existing methods. Furthermore, a simply verifiable condition for convergence is presented, which allows the straightforward evaluation of applicability. The proposed method is demonstrated by means of the linearization of a time-varying nonlinear amplifier, which highlights its capability of linearizing significantly distorted signals, illustrates the advantageous convergence behavior, and depicts its robustness against modeling errors

Evaluation of Fish and Macroinvertebrate Indices of Biotic Integrity in the Bioassessment of the Illinois River Basin

Evaluating performances of the fish and invertebrate Indices of Biotic Integrity (IBIs) for a region is important to maintain rigorous assessment of the environmental quality of streams, especially with increasing urbanization. Timing of the assessment is considered important, with the critical season (low flow, high temperature) preferred, but the primary season (spring– summer) may be as efficient. I assisted with the collection and analysis of fish and macroinvertebrates using methods developed by the United States Environmental Protection Agency’s (USEPA) Rapid Bioassessment Protocols (RBPs) and the Arkansas Department of Environmental Quality (ADEQ), along with obtaining habitat and chemical assessments during primary and critical periods during 2007-2009 at ten sites in the Illinois River Basin up and downstream of two wastewater treatment plants (WWTPs). My objectives were to (1) compare fish and macroinvertebrate IBIs for use in the Illinois River Basin; (2) investigate correlations with each IBI and its metrics to nutrient, habitat, and watershed variables; (3) compare the efficacy of the IBIs during both critical and primary seasons; and (4) determine how two WWTPs in the area affect downstream water quality into Oklahoma. The two IBIs were strongly correlated with each other (Rs of 0.59); however, macroinvertebrates outperformed the fish. More regionally specific fish metrics should allow for better performing fish IBIs, but adequate performance was found. Combining the seasons’ data allowed for a more comprehensive and statistically significant assessment; however, the primary season evaluated each site comparably to the combined data and generally outperformed the critical seasons. The combined and primary seasons’ macroinvertebrate IBIs revealed sites with lowered environmental quality below the WWTPs but with quick returns to reference conditions. My results indicate that it may be possible to test IBIs during only the primary seasons to get efficient water quality and site comparison assessments

Cohort Changes in the Transition from School to Work: What Changed and What Consequences Did it have for Wages?

This study examines the changes in the school-to-work transition in the United States over the latter part of the twentieth century and their consequences for the wages of young adults. In particular, we document the various types of work and schooling experiences acquired by youth who came to adulthood in the U.S. during the late 1960s, 1970s, and through the 1980s. We pay particular attention to how the differences across cohorts in these transitions vary by gender and race/ethnicity and how these differences affected their subsequent wage attainment. Evidence is evaluated using data from National Longitudinal Surveys of Young Women, Young Men, and Youth 1979. In general, we find that indicators of educational attainment, working while in school and non-school related work increased across cohorts for almost all racial/ethnic and gender groups. This was especially true for young women. Furthermore, various indicators of personal and family backgrounds changed in ways consistent with an improvement across cohorts in the preparation of young men and women for their attainment of schooling and work experience and their success in the labor market. The one exception to this general picture of improvement across cohorts was Hispanic men, who experienced a notable decline in educational attainment, the acquisition of full time work early in their adult lives and in a variety of personal and family background characteristics. With respect to hourly wage rates, we find that wages over the ages 16 through 27 declined across cohorts. However, the rate of growth of wages with age, particularly over adult ages, increased across cohorts for all racial/ethnic and gender groups, except black and Hispanic men. To assess the relative importance that changes in the school, work, military and other experiences had on wages across generations, we employ the decomposition proposed by Juhn, Murphy and Pierce (1993) to decompose the across-cohort wage changes in observable determinants, in their associated prices and in unobservable determinants, using a standard regression specification for the determinants of life cycle wages. We find that the dominant factor explaining the declines in wages across cohorts is attributable to changes in the prices of observable characteristics and to changes in unobservable determinants. At constant skill prices, changes in the skill composition across youth cohorts would have increased their wages, most especially for Hispanic women, followed by black women, white women, black men, and then white men. In striking contrast, Hispanic males’ wages would still have declined across cohorts purely accounting for compositional changes. We interpret this result as coming from the changing skill composition of immigrants. Our results also highlight the need for accounting for the endogeneity and selectivity of early skill acquisition.

The Impact of Regulations on the Supply and Quality of Care in Child Care Markets

We examine the impact of state child care regulations on the supply and quality of care in child care markets. We exploit panel data on both individual establishments and local markets to control for state, time, and, where possible, establishment-specific fixed effects to mitigate the potential bias due to policy endogeneity. We find that the imposition of regulations reduces the number of center-based child care establishments, especially in lower income markets. However, such regulations increase the quality of services provided, especially in higher income areas. Thus, there are winners and losers from the regulation of child care services.

HAL/S programmer's guide

HAL/S is a programming language developed to satisfy the flight software requirements for the space shuttle program. The user's guide explains pertinent language operating procedures and described the various HAL/S facilities for manipulating integer, scalar, vector, and matrix data types

Measuring Employment and Income for Low-Income Populations with Administrative and Survey Data

We discuss the strengths and weaknesses of income and employment data in national surveys, in unemployment insurance (UI) wage records, and in tax returns. The CPS, SIPP, NLS, and PSID surveys provide valuable information on the behavior of the low-income population. They have broad and fairly accurate measures of income for national samples, and their focus on families as the unit of analysis and their ease of access greatly enhance their value. The value of these data sets for evaluating welfare reform is severely limited, however. With the devolution of responsibility for TANF, the CPS and SIPP sampling frames and sample sizes mean that, at best, they can be only supplementary data sources for understanding the effects of welfare reform at the state and local levels. The apparent decline in program coverage in the CPS is also worrisome. UI data are available at the state level and can be matched to individuals in existing samples at relatively low cost. It is straightforward to do follow-up analyses on income and employment for workers who remain in the state, and UI data are timely. However, earnings are available only for individuals, while changes in family composition upon exit from welfare have been shown to have a large bearing on economic well-being. UI data do not allow us to track these changes. There also appears to be a substantial problem with some workers being classified as independent contractors and hence not entering the UI system. Overall gaps in coverage appear to be at least 13 percent and may be significantly higher. Even when wages are reported, there is some evidence that they are understated by a significant amount. We also present evidence on the degree to which tax data can be used to understand the incomes and employment of low-skilled workers. The paper concludes with brief recommendations for future research that might help fill some of the gaps we have identified.