The geological environment of the Shafton Seam and its effect on assessment of production capability

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Automatic control of a helicopter with a hanging load

An autopilot logic is designed here for controlling a helicopter with a hanging load. A 16th order model for the system is decoupled into four subsystems: (1) a second order system for yawing motion, (2) a second order system for vertical motion, (3) a sixth order system for longitudinal motion, and (4) a sixth order system for lateral motion. A measuring scheme, which could be used in remote areas, is developed and filters are designed to estimate the state variables from these measurements. The autopilot can be used to move the load over short distances without retracting the cables. This is done by automatically shifting the autopilot modes from position-hold (hover) to acceleration-hold to velocity-hold (cruise) to deceleration-hold to velocity-hold (near hover) to position-hold (hover). Use of such an autopilot might save considerable turnaround time. The Sikorsky S-61 helicopter is chosen as an example vehicle. The performance of the controlled system is studied in the presence of longitudinal and lateral winds

Particle filtering in high-dimensional chaotic systems

We present an efficient particle filtering algorithm for multiscale systems, that is adapted for simple atmospheric dynamics models which are inherently chaotic. Particle filters represent the posterior conditional distribution of the state variables by a collection of particles, which evolves and adapts recursively as new information becomes available. The difference between the estimated state and the true state of the system constitutes the error in specifying or forecasting the state, which is amplified in chaotic systems that have a number of positive Lyapunov exponents. The purpose of the present paper is to show that the homogenization method developed in Imkeller et al. (2011), which is applicable to high dimensional multi-scale filtering problems, along with important sampling and control methods can be used as a basic and flexible tool for the construction of the proposal density inherent in particle filtering. Finally, we apply the general homogenized particle filtering algorithm developed here to the Lorenz'96 atmospheric model that mimics mid-latitude atmospheric dynamics with microscopic convective processes.Comment: 28 pages, 12 figure

Youth-Adult Differences in the Demand for Unionization: Are American, British and Canadian Workers All That Different?

This paper examines demand for union membership amongst young workers in Britain, Canada and the United States. The paper benchmarks youth demands for collective representation against those of adult workers and finds that a large and significant representation gap exists in all three countries. Using a model of representation advanced by Farber (1982) and Riddell (1993) we find that a majority of the union density differential between young and adult workers is due to supply-side constraints rather than a lower desire for unionisation on the part of the young. This finding lends credence to two conjectures made in the paper; the first is that tastes for collective representation do not differ among workers (either by nationality or by age) and second that union representation can be fruitfully modelled as an experience good. The experience good properties of union membership explain the persistence of union density differentials amongst youth and adults both over time and across countries

Who calls the Tune at Work? The Impact of Trade Unions on Jobs and Pay

This report uses large-scale survey evidence to examine the effects of unions upon the employment levels of workplaces and upon the pay of their employees. Although some of the findings show that trade unions are associated with adverse outcomes, these effects are absent when employers jointly determine pay and employment matters with the unions