Experimental and Theoretical Research on Plasma Sheaths and Boundary Layers Around Stagnation Point Electrodes Semiannual Progress Report No. 3, 1 Jul. - 31 Dec. 1965

Plasma sheaths and boundary layers around stagnation point electrode

Hybrid fuzzy sliding mode control for motorised space tether spin-up when coupled with axial and torsional oscillation

A specialised hybrid controller is applied to the control of a motorised space tether spin-up space coupled with an axial and a torsional oscillation phenomenon. A seven-degree-of-freedom (7-DOF) dynamic model of a motorised momentum exchange tether is used as the basis for interplanetary payload exchange in the context of control. The tether comprises a symmetrical double payload configuration, with an outrigger counter inertia and massive central facility. It is shown that including axial and torsional elasticity permits an enhanced level of performance prediction accuracy and a useful departure from the usual rigid body representations, particularly for accurate payload positioning at strategic points. A simulation with given initial condition data has been devised in a connecting programme between control code written in MATLAB and dynamics simulation code constructed within MATHEMATICA. It is shown that there is an enhanced level of spin-up control for the 7-DOF motorised momentum exchange tether system using the specialised hybrid controller. hybrid controller

Dynamical modelling of the motorised momentum exchange tether incorporating axial elastic effects

A discretised planar tether model is proposed for the Motorised Momentum Exchange Tether (MMET) in which axial elasticity is accommodated. The model uses a generalised co-ordinate defining angular motion of the tether about its centre of mass, as it travels at constant velocity on a circular orbit in the Earth’s equatorial plane and a generalised coordinate depicting the elastic part of the tether length. The system comprises a symmetrical double payload configuration, with outrigger counter inertia, and it is shown that including axial elasticity permits an enhanced level of modelling accuracy for the tether both in librating and spinning modes. A simulation has been devised in MATLAB and SIMULINK for different data cases. This work will be used later within a spin-up control system and will act as a precursor for an in-depth study into the multi-scale dynamics of MMET tethers and space webs, on more complicated orbits. This, in turn, will be assimilated within new mission architectures

Characterization of the 4-canonical birationality of algebraic threefolds

In this article we present a 3-dimensional analogue of a well-known theorem of E. Bombieri (in 1973) which characterizes the bi-canonical birationality of surfaces of general type. Let $X$ be a projective minimal 3-fold of general type with $\mathbb{Q}$-factorial terminal singularities and the geometric genus $p_g(X)\ge 5$. We show that the 4-canonical map $\phi_4$ is {\it not} birational onto its image if and only if $X$ is birationally fibred by a family $\mathscr{C}$ of irreducible curves of geometric genus 2 with $K_X\cdot C_0=1$ where $C_0$ is a general irreducible member in $\mathscr{C}$.Comment: 25 pages, to appear in Mathematische Zeitschrif

ILR Impact Brief - Phased Retirement: Opportunities for Some but Not for All

Nearly three-quarters of employers surveyed indicate that some form of phased retirement could be worked out for white-collar employees aged 55 and older. Workers’ willingness to take advantage of this option, however, may diminish when employers\u27 terms and conditions are factored in. In other words, the majority of white-collar workers are presented with constrained opportunities for phased retirement when the possibility arises