39,403 research outputs found
Dual-spin attitude control for outer planet missions
The applicability of dual-spin technology to a Jupiter orbiter with probe mission was investigated. Basic mission and system level attitude control requirements were established and preliminary mechanization and control concepts developed. A comprehensive 18-degree-of-freedom digital simulation was utilized extensively to establish control laws, study dynamic interactions, and determined key sensitivities. Fundamental system/subsystem constraints were identified, and the applicability of dual-spin technology to a Jupiter orbiter with probe mission was validated
Alpha Surfaces for Complex Space-Times with Torsion
This paper studies necessary conditions for the existence of alpha-surfaces
in complex space-time manifolds with nonvanishing torsion. For these manifolds,
Lie brackets of vector fields and spinor Ricci identities contain explicitly
the effects of torsion. This leads to an integrability condition for
alpha-surfaces which does not involve just the self-dual Weyl spinor, as in
complex general relativity, but also the torsion spinor, in a nonlinear way,
and its covariant derivative. Interestingly, a particular solution of the
integrability condition is given by conformally right-flat and
right-torsion-free space-times.Comment: 7 pages, plain-tex, published in Nuovo Cimento B, volume 108, pages
123-125, year 199
Twistor Theory and Differential Equations
This is an elementary and self--contained review of twistor theory as a
geometric tool for solving non-linear differential equations. Solutions to
soliton equations like KdV, Tzitzeica, integrable chiral model, BPS monopole or
Sine-Gordon arise from holomorphic vector bundles over T\CP^1. A different
framework is provided for the dispersionless analogues of soliton equations,
like dispersionless KP or Toda system in 2+1 dimensions. Their
solutions correspond to deformations of (parts of) T\CP^1, and ultimately to
Einstein--Weyl curved geometries generalising the flat Minkowski space. A
number of exercises is included and the necessary facts about vector bundles
over the Riemann sphere are summarised in the Appendix.Comment: 23 Pages, 9 Figure
Future impacts of fresh water resource management: sensitivity of coastal deltas
We present an assessment of contemporary and future effective sealevel rise (ESLR) using a sample of 40 deltas distributed worldwide. For any delta, ESLR is a net rate defined by eustatic sea-level rise, natural gross rates of fluvial sediment deposition and subsidence, and accelerated subsidence due to groundwater and hydrocarbon extraction. Present-day ESLR, estimated from geospatial data and a simple model of deltaic dynamics, ranges from 0.5 to 12.5 mm year-1. Reduced accretion of fluvial sediment from upstream siltation of reservoirs and freshwater consumptive irrigation losses are primary determinants of ESLR in nearly 70% of the deltas, while for only 12% eustatic sea-level rise predominates. Future scenarios indicate a much larger impact on deltas than previously estimated. Serious challenges to human occupancy of deltas worldwide are conveyed by upland watershed factors, which have been studied less comprehensively than the climate change and sea-level rise question
Radiative corrections in processes at the SSC
We discuss radiative corrections for interactions in the SSC environment.
Based on the theory of Yennie, Frautschi and Suura, we develop appropriate
Monte Carlo event generators to compute the background electromagnetic
radiation. Our results indicate that multiple-photon effects must be taken into
account in the study of SSC physics such as Higgs decay.Comment: UTHEP-92-0901, 15 pages (incl. 3 figures), LaTeX (Talk presented at
the XXXII Cracow School of Theoretical Physics, Zakopane, June 1992
A Conservation of Resources Approach to Blackberry Use, Work-Family Conflict and Well-Being: Job Control and Psychological Detachment from Work as Potential Mediators
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