Real-time application of advanced three-dimensional graphic techniques for research aircraft simulation

Visual aids are valuable assets to engineers for design, demonstration, and evaluation. Discussed here are a variety of advanced three-dimensional graphic techniques used to enhance the displays of test aircraft dynamics. The new software's capabilities are examined and possible future uses are considered

The Quality Distribution of Jobs and the Structure of Wages in Search Equilibrium

When match formation is costly and wage determination is decentralized, privately optimal investments in job and worker quality diverge from socially efficient outcomes. To explore this issue, I consider search equilibrium environments with endogenous quality distributions for jobs and workers. I show that a search equilibrium with decentralized wage setting exhibits excessive relative supplies of inferior jobs and inferior workers. Moreover, there are fundamental tensions between the standard wage-setting condition for an efficient total supply of jobs (and workers) in two-sided search models and the conditions required for efficient mixes of jobs and workers. I also derive the efficient wage structure, contrast its properties to the decentralized wage structure and evaluate the welfare and productivity gains of moving to an efficient wage structure. Numerical exercises show that centralized bargaining between a labor union and an employer confederation over the structure of wages can improve productivity and welfare by compressing job-related wage differentials.

Induction of Interpretable Possibilistic Logic Theories from Relational Data

The field of Statistical Relational Learning (SRL) is concerned with learning probabilistic models from relational data. Learned SRL models are typically represented using some kind of weighted logical formulas, which make them considerably more interpretable than those obtained by e.g. neural networks. In practice, however, these models are often still difficult to interpret correctly, as they can contain many formulas that interact in non-trivial ways and weights do not always have an intuitive meaning. To address this, we propose a new SRL method which uses possibilistic logic to encode relational models. Learned models are then essentially stratified classical theories, which explicitly encode what can be derived with a given level of certainty. Compared to Markov Logic Networks (MLNs), our method is faster and produces considerably more interpretable models.Comment: Longer version of a paper appearing in IJCAI 201

Encoding Markov Logic Networks in Possibilistic Logic

Markov logic uses weighted formulas to compactly encode a probability distribution over possible worlds. Despite the use of logical formulas, Markov logic networks (MLNs) can be difficult to interpret, due to the often counter-intuitive meaning of their weights. To address this issue, we propose a method to construct a possibilistic logic theory that exactly captures what can be derived from a given MLN using maximum a posteriori (MAP) inference. Unfortunately, the size of this theory is exponential in general. We therefore also propose two methods which can derive compact theories that still capture MAP inference, but only for specific types of evidence. These theories can be used, among others, to make explicit the hidden assumptions underlying an MLN or to explain the predictions it makes.Comment: Extended version of a paper appearing in UAI 201

Tax Effects on Work Activity, Industry Mix and Shadow Economy Size: Evidence from Rich-Country Comparisons

Guided by a simple theory of task assignment and time allocation, we investigate the long run response to national differences in tax rates on labor income, payrolls and consumption. The theory implies that higher tax rates reduce work time in the market sector, increase the size of the shadow economy, alter the industry mix of market activity, and twist labor demand in a way that amplifies negative effects on market work and concentrates effects on the less skilled. We also describe conditions whereby cross-country OLS regressions yield unbiased estimates of the total effect of taxes, inclusive of indirect effects that work through government spending responses to tax revenues. Regressions on rich-country samples in the mid 1990s indicate that a unit standard deviation tax rate difference of 12.8 percentage points leads to 122 fewer market work hours per adult per year, a drop of 4.9 percentage points in the employment-population ratio, and a rise in the shadow economy equal to 3.8 percent of GDP. It also leads to 10 to 30 percent lower employment and value added shares in (a) retail trade and repairs, (b) eating, drinking and lodging, and (c) a broader industry group that includes wholesale and motor trade.

Occupation-Level Income Shocks and Asset Returns: Their Covariance and Implications for Portfolio Choice

This paper develops and applies a simple graphical approach to portfolio selection that accounts for covariance between asset returns and an investor's labor income. Our graphical approach easily handles income shocks that are partly hedgable, multiple risky assets, many periods and life cycle considerations. We apply the approach to occupation-level components of individual income innovations estimated from repeated cross sections of the Current Population Survey. We characterize several properties of these innovations, including their covariance with aggregate equity returns, long-term bond returns and returns on several other assets. Aggregate equity returns are uncorrelated with the occupation-level income innovations, but a portfolio formed on firm size is significantly correlated with income innovations for several occupations, and so are selected industry-level equity portfolios. An application of the theory to the empirical results shows (a) large predicted levels of risky asset holdings compared to observed levels, (b) considerable variation in optimal portfolio allocations over the life cycle, and (c) large departures from the two-fund separation principle.