20,699 research outputs found
Compressible laminar streaks with wall suction
Peer reviewedPublisher PD
Supersolutions
We develop classical globally supersymmetric theories. As much as possible,
we treat various dimensions and various amounts of supersymmetry in a uniform
manner. We discuss theories both in components and in superspace. Throughout we
emphasize geometric aspects. The beginning chapters give a general discussion
about supersymmetric field theories; then we move on to detailed computations
of lagrangians, etc. in specific theories. An appendix details our sign
conventions. This text will appear in a two-volume work "Quantum Fields and
Strings: A Course for Mathematicians" to be published soon by the American
Mathematical Society. Some of the cross-references may be found at
http://www.math.ias.edu/~drm/QFT/Comment: 130 pages, AMSTe
The impact of local masses and inertias on the dynamic modelling of flexible manipulators
After a brief review of the recent literature dealing with flexible multi-body modelling for control design purpose, the paper first describes three different techniques used to
build up the dynamic model of SECAFLEX, a 2 d.o.f. flexible in-plane manipulator driven by geared DC motors : introduction of local fictitious springs, use of a basis of assumed Euler-Bernouilli cantilever-free modes and of 5th order polynomial modes. This last technique allows to take easily into account local masses and inertias, which appear important in real-life experiments. Transformation of the state space models obtained in a common modal basis allows a quantitative comparison of the results obtained, while Bode plots of the various interesting transfer functions relating input torques to output in-joint and tip mea-surements give rather qualitative results. A parametric study of the effect of angular configuration changes and physical parameter modifications (including the effect of rotor inertia) shows that the three techniques give similar results up to the first flexible modes of each link when concentrated masses and inertias are present. From the control point of view, “pathological” cases are exhibited : uncertainty in the phase of the non-colocated transfer functions, high dependence of the free modes in the rotor inertia value. Robustness of the control to these kinds of uncertainties appears compulsory
On Fibonacci Knots
We show that the Conway polynomials of Fibonacci links are Fibonacci
polynomials modulo 2. We deduce that, when n \not\equiv 0 \Mod 4 and the Fibonacci knot \cF_j^{(n)} is not a Lissajous knot.Comment: 7p. Sumitte
Chebyshev Knots
A Chebyshev knot is a knot which admits a parametrization of the form where are
pairwise coprime, is the Chebyshev polynomial of degree and \phi
\in \RR . Chebyshev knots are non compact analogues of the classical Lissajous
knots. We show that there are infinitely many Chebyshev knots with
We also show that every knot is a Chebyshev knot.Comment: To appear in Journal of Knot Theory and Ramification
Flexible joint control : robustness analysis of the collocated and non-collocated feedbacks
In this paper, we propose a discussion on the robustness and performance properties of a proportional-derivative controller applied to a very flexible joint. Because of the flexible mode due to in-joint compliance, the classical collocated control does not allow to obtain good rigid mode dynamics with a correct phase margin in low and high frequency, and the non-collocated control does not allow to
damp correctly the rotor mode. The simultaneous analysis of discrete root loci and Nichols plots leads to a phase control law with a derivative term built from both input and output velocities. Simulations taking into account various real non-linearities and measurement imperfections are proposed to validate this improved control design
- …