2,128 research outputs found
John P. MacLean portrait
No full textPhotograph of Ohio author John P. MacLean (1848-1939). MacLean was born in Franklin, Ohio, and is remembered as a Universalist minister, historian and archaeologist. In addition to writings on Scottish history and the Shakers, his work included the books "A Manual of the Antiquity of Man" (1877), "The Mound Builders" (1879) and "Mastodon, Mammoth and Man" (1880)
John P. MacLean portrait
No full textPhotograph of Ohio author John P. MacLean (1848-1939). MacLean was born in Franklin, Ohio, and is remembered as a Universalist minister, historian and archaeologist. In addition to writings on Scottish history and the Shakers, his work included the books "A Manual of the Antiquity of Man" (1877), "The Mound Builders" (1879) and "Mastodon, Mammoth and Man" (1880)
Season 1, Episode 10: Maclean
No full textMaclean. The name is synonymous with many things: great writing, fishing, and fire to name just a few. On this, the tenth and final episode of season one, author John Maclean joins the podcast, along with University of Montana researcher Brent Ruby and host Charlie Palmer to discuss South Canyon, the history of hotshots, and John’s current book project on the Yarnell Hill fire that killed nineteen Granite Mountain Hotshots.https://scholarworks.umt.edu/ontheline_podcasts/1009/thumbnail.jp
Still room for improvement? The educational experiences of looked after children in Scotland
No full textIn this chapter Kirstie Maclean and Graham Connelly present an analysis of joined-up thinking in Scotland from both social services and education perspectives
Attitude motion planning for a spin stabilised disk sail
No full textWhile solar sails are capable of providing continuous low thrust propulsion the size and flexibility of the sail structure poses difficulties to their attitude control. Rapid slewing of the sail can cause excitation of structural modes, resulting in flexing and oscillation of the sail film and a subsequent loss of performance and decrease in controllability. Disk shaped solar sails are particularly flexible as they have no supporting structure and so these spacecraft must be spun around their major axis to stiffen the sail membrane via the centrifugal force. In addition to stiffening the structure this spin stabilisation also provides gyroscopic stiffness to disturbances, aiding the spacecraft in maintaining its desired attitude. A method is applied which generates smooth reference motions between arbitrary orientations for a spin-stabilised disk sail. The method minimises the sum square of the body rates of the spacecraft, therefore ensuring that the generated attitude slews are slow and smooth, while the spin stabilisation provides gyroscopic stiffness to disturbances. An application of Pontryagin’s maximum principle yields an optimal Hamiltonian which is completely solvable in closed form. The resulting analytical expressions are a function of several free parameters enabling parametric optimisation to be used to provide reference motions which match prescribed boundary conditions on the initial and final configurations. The generated reference motions are utilised in the repointing of a 70m radius spin-stabilised disk solar sail in a heliocentric orbit, with the aim of assessing the feasibility of the motion planning method in terms of the control torques required to track the motions
A recognition theorem for polynomial growth outer automorphisms of the free group
No full textFeighn and Handel’s recognition theorem for Out(F_n) provides invariants that canonically determine any forward rotationless outer automorphism of the free group. We ask to what extent those invariants can be extended to outer automorphisms with some periodic behavior. Many of the same constructions do not have natural analogs, in particular because of the possible lack of principal representatives in this setting. However, by restricting our attention to polynomial growth outer automorphisms and using train track technology, we are able to find a special set of lines in the free group that encode all the dynamical information of these non-forward rotationless maps.Ph. D.Includes bibliographical referencesIncludes vitaby By Gregory MacLean Schinke Fei
Matthew S. Weinert on A Decade of Human Security: Global Governance and New Multilateralism by Sandra MacLean, David Black, and Timothy Shaw. Aldershot, UK: Ashgate, 2006. 264 pp.
No full textA review of:
A Decade of Human Security: Global Governance and New Multilateralism by Sandra MacLean, David Black, and Timothy Shaw. Aldershot, UK: Ashgate, 2006. 264 pp
Heteroclinic optimal control solutions for attitude motion planning
No full textAn analytical attitude motion planning method is presented that exploits the heteroclinic connections of an optimal kinematic control problem. This class of motion, of hyperbolic type, supply a special case of analytically defined rotations that can be further optimised to select a suitable reference motion that minimises accumulated torque and the final orientation error amongst these motions. This analytical approach could be used to improve the overall performance of a spacecraft’s attitude dynamics and control system when used alongside current flight tested tracking controllers. The resulting algorithm only involves optimising a small number of parameters of standard functions and is simple to implement
A new approach to the solution of free rigid body motion for attitude manoeuvers
No full textA Hamiltonian formulation of free rigid body motion defined on the Special Unitary Group SU(2) is used to integrate the system to obtain a convenient quaternion representation for attitude engineering applications. Novel content of this paper concerns applying a modern approach, based on geometric control theory to obtain the kinematic solution in an elegant and compact form. Moreover, this integration leads to an attitude representation which is not Euler-angle-like, thus enhancing its applicability (e.g. to attitude motion design)
Planning natural repointing manoeuvres for nano-spacecraft
No full textIn this paper the natural dynamics of a rigid body are exploited to plan attitude manoeuvres for a small spacecraft. By utilising the analytical solutions of the angular velocities and making use of Lax pair integration, the time evolution of the attitude of the spacecraft in a convenient quaternion form is derived. This enables repointing manoeuvres to be generated by optimising the free parameters of the analytical expressions, the initial angular velocities of the spacecraft, to match prescribed boundary conditions on the final attitude of the spacecraft. This produces reference motions which can be tracked using a simple proportional-derivative controller. The natural motions are compared in simulation to a conventional quaternion feedback controller and found to require lower accumulated torque. A simple obstacle avoidance algorithm, exploiting the analytic form of natural motions, is also described and implemented in simulation. The computational efficiency of the motion planning method is discussed
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