Distributed cooperative trajectory generation for multiple autonomous vehicles using Pythagorean Hodograph Bézier curves

This dissertation presents a framework for multi-vehicle trajectory generation that enables efficient computation of sets of feasible, collision-free trajectories for teams of autonomous vehicles executing cooperative missions with common objectives. Existing methods for multi-vehicle trajectory generation generally rely on discretization in time or space and, therefore, ensuring safe separation between the paths comes at the expense of an increase in computational complexity. On the contrary, the proposed framework is based on a three-dimensional geometric-dynamic approach that uses continuous Bézier curves with Pythagorean hodographs, a class of polynomial functions with attractive mathematical properties and a collection of highly efficient computational procedures associated with them. The use of these curves is critical to generate cooperative trajectories that are guaranteed to satisfy minimum separation distances, a key feature from a safety standpoint. By the differential flatness property of the dynamic system, the dynamic constraints can be expressed in terms of the trajectories and, therefore, in terms of Bézier polynomials. This allows the proposed framework to efficiently evaluate and, hence, observe the dynamic constraints of the vehicles, and satisfy mission-specific assignments such as simultaneous arrival at predefined locations. The dissertation also addresses the problem of distributing the computation of the trajectories over the vehicles, in order to prevent a single point of failure, inherently present in a centralized approach. The formulated cooperative trajectory-generation framework results in a semi-infinite programming problem, that falls under the class of nonsmooth optimization problems. The proposed distributed algorithm combines the bundle method, a widely used solver for nonsmooth optimization problems, with a distributed nonlinear programming method. In the latter, a distributed formulation is obtained by introducing local estimates of the vector of optimization variables and leveraging on a particular structure, imposed on the local minimizer of an equivalent centralized optimization problem

Do low survey response rates bias results? Evidence from Japan

BACKGROUND In developed countries, response rates have dropped to such low levels that many in the population field question whether the data can provide unbiased results. OBJECTIVE The paper uses three Japanese surveys conducted in the 2000s to ask whether low survey response rates bias results. A secondary objective is to bring results reported in the survey response literature to the attention of the demographic research community. METHODS Using a longitudinal survey as well as paradata from a cross-sectional survey, a variety of statistical techniques (chi square, analysis of variance (ANOVA), logistic regression, ordered probit or ordinary least squares regression (OLS), as appropriate) are used to examine response-rate bias. RESULTS Evidence of response-rate bias is found for the univariate distributions of some demographic characteristics, behaviors, and attitudinal items. But when examining relationships between variables in a multivariate analysis, controlling for a variety of background variables, for most dependent variables we do not find evidence of bias from low response rates. CONCLUSIONS Our results are consistent with results reported in the econometric and survey research literatures. Low response rates need not necessarily lead to biased results. Bias is more likely to be present when examining a simple univariate distribution than when examining the relationship between variables in a multivariate model. COMMENTS The results have two implications. First, demographers should not presume the presence or absence of low response-rate biasrather they should test for it in the context of a specific substantive analysis. Second, demographers should lobby data gatherers to collect as much paradata as possible so that rigorous tests for low response-rate bias are possible

Nontraditional Family-Related Attitudes in Japan: Macro and Micro Determinants

Attitudinal data are commonly used to measure values, which in turn represent moral doctrines that are resistant to change and are the foundation for societal norms. This article examines changes in the attitudinal climate in Japan. Three national surveys (1994, 2000, and 2009) are used to examine a range of attitudes that measure a) the centrality of marriage and childbearing, b) nontraditional family behaviors, and c) gender roles in the work and family spheres. There is strong evidence of movement toward less-traditional attitudes during 1994–2000, followed by limited change in the 2000s. Period factors were paramount in the 1990s. Across the board, women hold less-traditional attitudes than men, and this difference has increased over time. Both engaging in nontraditional family behaviors (being married but remaining childless) and knowing someone who has engaged in nontraditional family behaviors (cohabitation) causally lead to holding nontraditional attitudes, suggesting mechanisms whereby changes in individual behavior can lead to changes in societal values

Employment and household tasks of Japanese couples, 1994-2009

The paper examines changes in the relationship between employment and household tasks of Japanese couples, using data drawn from national cross-sectional surveys in 1994, 2000 and 2009 of persons aged 20–49 and from the 2009 follow-up of the 2000 survey. Wives’ employment is structured by their husbands’ employment time and earning power, as well as by their family situations including the presence and age of children and coresidence with parents. Housework hours of husbands, though very low, increased over time, while wives’ hours decreased. Wives housework time decreases as their employment time increases. Marriage dramatically increases women’s housework time but produces little change in men’s time. Husbands’ housework hours are positively correlated with reported marital satisfaction of both spouses

A Safe Cooperative Framework for Atmospheric Science Missions with Multiple Heterogeneous UAS using Piecewise Bezier Curves

Autonomous operation of UAS holds promise for greater productivity of atmospheric science missions. However, several challenges need to be overcome before such missions can be made autonomous. This paper presents a framework for safe autonomous operations of multiple vehicles, particularly suited for atmospheric science missions. The framework revolves around the use of piecewise Bezier curves for trajectory representation, which in conjunction with path-following and time-coordination algorithms, allows for safe coordinated operations of multiple vehicles

Order amidst change: Work and family trajectories in Japan

Substantial family and work macro-level change has been occurring in Japan. Examples include a decline in the availability of jobs that afford lifetime protection against unemployment, an increase in jobs that do not carry benefits such as a pension, an increase in age at marriage and at first birth, and an increase in marital dissolution. Using life history data from the 2000 National Survey on Family and Economic Conditions, young Japanese appear to have responded to these macro-level changes in a fairly orderly manner. Marriage and childbearing have been postponed, but marriage still precedes childbearing. Education is completed prior to starting work. For men, once work commences they continue working. For women, the classic conflict between work and family roles is evident. For men and women in both the family and work spheres Japanese young adults have more orderly life course trajectories than American young adults

2007 Annual progress report synopsis of the Center for Structures of Membrane Proteins

A synopsis of the 2007 annual progress report for the Center for Structures of Membrane Proteins, a specialized center of the Protein Structure Initiative

Neural and Synaptic Defects in slytherin, a Zebrafish Model for Human Congenital Disorders of Glycosylation

Congenital disorder of glycosylation type IIc (CDG IIc) is characterized by mental retardation, slowed growth and severe immunodeficiency, attributed to the lack of fucosylated glycoproteins. While impaired Notch signaling has been implicated in some aspects of CDG IIc pathogenesis, the molecular and cellular mechanisms remain poorly understood. We have identified a zebrafish mutant slytherin (srn), which harbors a missense point mutation in GDP-mannose 4,6 dehydratase (GMDS), the rate-limiting enzyme in protein fucosylation, including that of Notch. Here we report that some of the mechanisms underlying the neural phenotypes in srn and in CGD IIc are Notch-dependent, while others are Notch-independent. We show, for the first time in a vertebrate in vivo, that defects in protein fucosylation leads to defects in neuronal differentiation, maintenance, axon branching, and synapse formation. Srn is thus a useful and important vertebrate model for human CDG IIc that has provided new insights into the neural phenotypes that are hallmarks of the human disorder and has also highlighted the role of protein fucosylation in neural development