Direct use of linear time-domain aerodynamics in aeroservoelastic analysis: Aerodynamic model

The work presented here is the first part of a continuing effort to expand existing capabilities in aeroelasticity by developing the methodology which is necessary to utilize unsteady time-domain aerodynamics directly in aeroservoelastic design and analysis. The ultimate objective is to define a fully integrated state-space model of an aeroelastic vehicle's aerodynamics, structure and controls which may be used to efficiently determine the vehicle's aeroservoelastic stability. Here, the current status of developing a state-space model for linear or near-linear time-domain indicial aerodynamic forces is presented

An Economist's Guide to U.S. v. Microsoft

We analyze the central economic issues raised by U.S. v Microsoft. Network effects and economies of scale in applications programs created a barrier to entry for new operating system competitors, which the combination of Netscape Navigator and the Java programming language potentially could have lowered. Microsoft took actions to eliminate this threat to its operating system monopoly, and some of Microsoft's conduct very likely harmed consumers. While we recognize the risks of the government's proposed structural remedy of splitting Microsoft in two, we are pessimistic that a limited conduct remedy would be effective in this case.

Market Structure, Organizational Structure, and R&D Diversity

We examine the effects of market structure and the internal organization of firms on equilibrium R&D projects. We compare a monopolist's choice of R&D portfolio to that of a welfare maximizer. We next show that Sah and Stiglitz's finding that the market portfolio of R&D is independent of the number of firms under Bertrand competition extends to neither Cournot oligopoly nor a cartel. We also show that the ability of firms to pre-empt R&D by rivals along particular research paths can lead to socially excessive R&D diversification. Lastly, using Sah and Stiglitz's definition of hierarchy, we establish conditions under which larger hierarchies invest in smaller portfolios.

Nonlinear control of an industrial robot

The precise control of a robot manipulator travelling at high speed constitutes a major research challenge. This is due to the nonlinear nature of the dynamics of the arm which make many traditional, linear control methodologies inappropriate. An alternative approach is to adopt controllers which are themselves nonlinear. Variable structure control systems provide the possibility of imposing dynamic characteristics upon a poorly modelled and time varying system by means of a discontinuous control signal. The basic algorithm overcomes some nonlinear effects but is sensitive to Coulomb friction andactuator saturation. By augmenting this controller with compensation terms, these effects may largely be eliminated.In order to investigate these ideas, a number of variable structure control systems ~re applied to a low cost industrial robot having a highly nonlinear and flexible drive system. By a combination of hardware enhancements and control system developments, an improvement in speed by a factor of approximately three was achieved while the trajectory tracking accuracy was improved by a factor of ten, compared with the manufacturer's control system.In order to achieve these improvements, it was necessary to develop a dynamic model of the arm including the effects of drive system flexibility and nonlinearities. The development of this model is reported in this thesis, as is work carried out on a comparison of numerical algorithms for the solution of differential equations with discontinuous right hand sides, required in the computer aided design of variable structure control systems

Product improvement and technological tying in a winner-take-all market

In a winner-take-all duopoly market for systems in which firms invest to improve their products, a monopoly supplier of an essential system component may have an incentive to advantage itself by technological tying; that is, by designing the component to work better in its own system. If the vertically integrated firm is prevented from technologically tying, then there is a pure strategy equilibrium in which the more efficient firm invests and serves the entire market. However other equilibria may exist, including a pure strategy equilibrium in which the less efficient firm invests and captures the market and mixed strategy equilibria in which each firm captures the market with positive probability. In contrast, if the vertically integrated firm is able to degrade the quality of its rival's system with a technological tie, and if the wholesale price of the essential component is insufficiently remunerative, then there is a unique equilibrium outcome in which the supplier of the essential component invests alone and forecloses a more efficient rival with an actual, or merely threatened, technological tie. A comparison of these equilibria for the two game forms demonstrates that a prohibition of technological tying can either increase or decrease social welfare depending on equilibrium selection

Evaluation of high performance LMFBR blanket configurations

Substantially the same as a Ph. D. thesis by G.J. Brown in the Dept. of Nuclear Engineering, MIT, 1974Includes bibliographical references (pages 249-254)AEC Contract AT(11-1)-225

Bicycle rack

A bicycle rack designed to support and lock a bicycle by the bicycle\u27s front center post. Support and lock brackets for individual bicycles are horizontally disposed fork arrangements formed by two joined U-shaped members. Oppositely extending locking brackets allow pairs of bicycles to be conveniently placed along a series of evenly spaced posts and cross-bars

A Search for Water in the Atmosphere of HAT-P-26b Using LDSS-3C

The characterization of a physically-diverse set of transiting exoplanets is an important and necessary step towards establishing the physical properties linked to the production of obscuring clouds or hazes. It is those planets with identifiable spectroscopic features that can most effectively enhance our understanding of atmospheric chemistry and metallicity. The newly-commissioned LDSS-3C instrument on Magellan provides enhanced sensitivity and suppressed fringing in the red optical, thus advancing the search for the spectroscopic signature of water in exoplanetary atmospheres from the ground. Using data acquired by LDSS-3C and the Spitzer Space Telescope, we search for evidence of water vapor in the transmission spectrum of the Neptune-mass planet HAT-P-26b. Our measured spectrum is best explained by the presence of water vapor, a lack of potassium, and either a high-metallicity, cloud-free atmosphere or a solar-metallicity atmosphere with a cloud deck at ~10 mbar. The emergence of multi-scale-height spectral features in our data suggests that future observations at higher precision could break this degeneracy and reveal the planet's atmospheric chemical abundances. We also update HAT-P-26b's transit ephemeris, t_0 = 2455304.65218(25) BJD_TDB, and orbital period, p = 4.2345023(7) days.Comment: 9 pages, 8 figures, Accepted for publication in Ap