The double universal joint wrist on a manipulator: Solution of inverse position kinematics and singularity analysis

This paper presents three methods to solve the inverse position kinematics position problem of the double universal joint attached to a manipulator: (1) an analytical solution for two specific cases; (2) an approximate closed form solution based on ignoring the wrist offset; and (3) an iterative method which repeats closed form position and orientation calculations until the solution is achieved. Several manipulators are used to demonstrate the solution methods: cartesian, cylindrical, spherical, and an anthropomorphic articulated arm, based on the Flight Telerobotic Servicer (FTS) arm. A singularity analysis is presented for the double universal joint wrist attached to the above manipulator arms. While the double universal joint wrist standing alone is singularity-free in orientation, the singularity analysis indicates the presence of coupled position/orientation singularities of the spherical and articulated manipulators with the wrist. The cartesian and cylindrical manipulators with the double universal joint wrist were found to be singularity-free. The methods of this paper can be implemented in a real-time controller for manipulators with the double universal joint wrist. Such mechanically dextrous systems could be used in telerobotic and industrial applications, but further work is required to avoid the singularities

Three-dimensional boundary layers approaching separation

The theory of semi-similar solutions of the laminar boundary layer equations is applied to several flows in which the boundary layer approaches a three-dimensional separation line. The solutions obtained are used to deduce the nature of three-dimensional separation. It is shown that in these cases separation is of the "ordinary" type. A solution is also presented for a case in which a vortex is embedded within the three-dimensional boundary layer

Neotropical Bird Migration During The Ice Ages: Orientation And Ecology

Reconstruction of breeding habitat of North American Neotropical migrants 18,000 years ago and 9,000 years ago indicated major shifts in both location and composition of plant communities relative to present conditions. Increased vegetation in xeric areas may have compensated, at least in part, for the reduction in breeding habitat due to glaciation. Autumnal flights of Neotropical passerine migrants flying on constant headings from North America to Central and South America were simulated under present wind conditions and for winds during periods of glaciation at 18,000 and 9,000 years ago. The 155 degrees average headings currently observed for Atlantic migrants were found to function well during periods of glaciation and may have been more generally useful during those times than at present

The effect of variable rest intervals and chronic ankle instability on triplanar ankle motion during performance of the Star Excursion Balance Test

Inadequate rest intervals may contribute to impaired performance during functional tests. However, the effect of different rest intervals on performance of the SEBT in individuals with and without CAI is not known. Our purposes were to determine whether different rest intervals impact ankle kinematics during the SEBT and whether there differences between those two populations. 24 controls and 24 CAI completed 3 trials in 3 reach directions (anteromedial; AM, medial; M, posteromedial; PM). The order of rest intervals and reach distance were randomized and counterbalanced. Three visits were required to complete the 3 rest interval conditions (10, 20, 40 s). Rest interval did not impact ankle kinematics between controls and CAI during the SEBT. Dorsiflexion (DF) (AM:partial eta(2) = 0.18; M:partial eta(2) = 0.23; PM:partial eta(2) = 0.23) for all directions and tibial internal rotation (TIR) excursions (AM:partial eta(2) = 0.20) for AM direction were greater in individuals with CAI regardless of rest interval length. Rest intervals ranging from 10 to 40 s did not influence ankle kinematics. Differences exist in DF and TIR between controls and CAI during the SEBT. These findings suggest that clinicians can use any rest interval between 10 and 40 s when administrating the SEBT. However, triplanar motion differs during a complex functional movement in controls compared to CAI

Estimates from a Consumer Demand System: Implications for the Incidence of Environmental Taxes

Most studies suggest that environmental taxes are regressive, and thus are unattractive policy options. We consider the distributional effects of a gasoline tax increase using three welfare measures and under three scenarios for gas tax revenue use. To incorporate behavioral responses we use Consumer Expenditure Survey data to estimate a consumer demand system that includes gasoline, other goods, and leisure. We find that the gas tax is regressive, but that returning the revenue through a lump-sum transfer more than offsets this, yielding a net increase in progressivity. We also find that ignoring behavioral changes in distributional calculations overstates both the overall burden of the tax and its regressivity.

When Can Carbon Abatement Policies Increase Welfare? The Fundamental Role of Distorted Factor Markets

This paper employs analytical and numerical general equilibrium models to assess the efficiency impacts of two policies to reduce U.S. carbon emissions — a revenue-neutral carbon tax and a non-auctioned carbon quota — taking into account the interactions between these policies and pre-existing tax distortions in factor markets. We show that tax interactions significantly raise the costs of both policies relative to what they would be in a first-best setting. In addition, we show that these interactions put the carbon quota at a significant efficiency disadvantage relative to the carbon tax: for example, the costs of reducing emissions by 10 percent are more than three times as high under the carbon quota as under the carbon tax. This disadvantage reflects the inability of the quota policy to generate revenue that can be used to reduce pre-existing distortionary taxes. Indeed, second-best considerations can limit the potential of a carbon quota to generate overall efficiency gains. Under our central values for parameters, a non-auctioned carbon quota (or set of grandfathered carbon emissions permits) cannot increase efficiency unless the marginal benefits from avoided future climate change are at least $17.8 per ton of carbon abatement. Most estimates of marginal environmental benefits are below this level. Thus, our analysis suggests that any carbon abatement by way of a non-auctioned quota will reduce efficiency. In contrast, our analysis indicates that a revenue-neutral carbon tax can be efficiency-improving so long as marginal environmental benefits are positive.

The Usual Excess-Burden Approximation Usually Doesn't Come Close

This paper shows that the usual excess-burden triangle' formula performs poorly when used to assess the excess burden from taxes on intermediate inputs or consumer goods, and derives a practical alternative to this formula. We use an analytically tractable general equilibrium model to reveal how interactions with pre-existing taxes in other markets critically affect the excess burden of new taxes on intermediate inputs or consumer goods. The usual excess-burden formula ignores these interactions, and consequently yields highly inaccurate assessments of excess burden. Prior economic theory implicitly acknowledges the relevance of general-equilibrium interactions to excess burden, but does not indicate which interactions are most important or reveal the fundamental (first-order) contribution of these interactions. Moreover, prior studies do not offer a practical alternative to the usual excess-burden approximation. This paper helps fill the gap between theory and practice. First, it shows analytically that the importance of the interaction with a given pre-existing tax is roughly proportional to the amount of revenue raised by that tax. Second, the paper derives a practical alternative formula for approximating the excess burden from a commodity tax. Finally, it performs numerical simulations to illustrate the significance of adopting our alternative to the usual approximation formula. For realistic parameter values and a wide range of assumed rates for prior taxes, the usual formula captures less than half of the excess burden of taxes on commodities. When the rate of the new tax is small,' this formula captures less than five percent of the true excess burden. In contrast, the alternative approximation formula derived here yields estimates that are consistently within five percent of the actual excess burden.

Empirical Estimates for Environmental Policy Making in a Second- Best Setting

This study estimates parameters necessary to calculate the optimal second-best gasoline tax, most notably the cross-price elasticity between gasoline and leisure. Prior work indicates that in a second-best setting with distortionary income taxes, both the cost of environmental regulation and the optimal environmental tax rate depend crucially on the cross-price elasticity between a polluting good and leisure. However, no prior study on second-best environmental regulation has estimated this elasticity. Using household data, we find that gasoline is a relative complement to leisure, and thus that the optimal gasoline tax is significantly higher than marginal damages–the opposite of the result suggested by the prior literature. Following this approach to estimate cross-price elasticities with leisure for other major polluting goods could strongly influence estimates of optimal environmental taxes.second-best environmental taxes, optimal taxes, tax interactions, demand system

A Simple Model of Optimal Hate Crime Legislation

We present a simple model of the effects of hate crime legislation. It shows that even if the direct harm to victims of hate crime is the same as for other crimes, because of other differences in the effects it may still be optimal to exert more law-enforcement effort to deter or prevent hate crime. These differences also have previously unrecognized effects on the optimal level of effort by potential hate crime victims to avoid being victimized, thus affecting the efficiency of government policies that encourage or discourage such effort. We discuss the implications of these results for optimal hate-crime policy, as well as for policy toward other similar crimes, such as terrorism.

Comparison of toughened composite laminates using NASA standard damage tolerance tests

The proposed application of composite materials to transport wing and fuselage structures prompted the search for tougher materials having improved resistance to impact damage and delamination. Several resin/graphite fiber composite materials were subjected to standard damage tolerance tests and the results were compared to ascertain which materials have superior toughness. In addition, test results from various company and NASA laboratories were compared for repeatability