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Haifa, Israel

Djerassi S.,Rafael Laboratories
Multibody System Dynamics | Year: 2016

This work addresses the ‘hard collision’ approach to the solution of planar, simple non-holonomic systems undergoing a one-point collision-with-friction problem, showing that (i) there are no coherent types of collision whereby forward sliding follows sticking, unless the initial relative tangential velocity of the colliding points vanishes; and (ii) the type of collision can be determined directly, given the collision angle of incidence (Formula presented.) and Coulomb’s coefficient of friction (Formula presented.) between the colliding points. The classic hitting rod problem is used to illustrate the (Formula presented.)–(Formula presented.) collision-type dependence. Finally, the relation between collision with friction and tangential impact problems in multibody systems is briefly discussed. © 2016 Springer Science+Business Media Dordrecht Source


Luttwak G.,Rafael Laboratories | Falcovitz J.,Hebrew University of Jerusalem
Computers and Fluids | Year: 2013

A recently formulated frame-invariant monotonicity criterion and slope limiter for vectors was applied to the Staggered Mesh Godunov-SMG/Q scheme for Lagrangian and ALE hydrodynamics. The VIP (vector-space polygon or polyhedron) was shown to be a natural extension of monotonicity constraints from scalar to vector variables. Taking notice of the fact that gradients of scalars are vectors, we now seek to use this new concept to devise better, and perhaps truly multidimensional, slope limiters for scalar variables. The proposed scheme constitutes a generalization of a 1D monotonic-averaging limiter for scalars, to a VIP type limiter for (vector) gradients of scalars in 2D or 3D. Test cases computed by the SMG/ALE scheme, using the new VIP limiter for gradients, are presented. As we can see from them, the new method, while being robust in strong shock computations, can better preserve gradients of density under advection. © 2012 Elsevier Ltd. Source


Rusnak I.,Rafael Laboratories
Journal of Guidance, Control, and Dynamics | Year: 2010

In preliminary analysis of guided systems, it is required to assess the miss distance performance from some small set of parameters. This paper presents analytical formulas of bounds on the achievable rms miss by a radar-guided missile against a variety of target maneuvers. These formulas use a set of core parameters that affect the miss distance; thus, they can be used for synthesis and analysis of the performance of radar-guided tactical missiles. The bound is derived, subject to the assumption that the missile guidance law and estimator are fully matched to the missile dynamics, the target maneuver, and the glint noise. The glint is the dominant noise source, the missile applies frequency agility, and there is no missile acceleration limit. No system can achieve smaller rms miss distance than the one presented, subject to the stated assumptions. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. Source


Marcus S.W.,Rafael Laboratories
IEEE Transactions on Antennas and Propagation | Year: 2013

The optical transformation is generally used to deform free space in order to obtain novel effects on waves. Such effects can be realized by replacing the deformed region by a 'metamaterial' characterized by ε and μ tensors that are determined by the transformation. A new type of transformation is proposed which not only deforms a free space region, but transforms a non-trivially shaped conducting surface that bounds this region as well. The deformations are designed to map the original region into a planar slab of metamaterial, and to map the conducting surface into a plate which bounds this slab. Since the fields outside the deformed region-which include the fields scattered by the original conducting surface-are unaffected by the transformation, they can, in effect, be produced by scattering from the planar metamaterial-coated plate created from the transformation. This substitution of a non-trivially shaped conducting surface by a planar metamaterial-coated plate is applied to (a) a face of a wedge to produce reflection from the planar metamaterial-coated plate that is not in the specular direction, and (b) a parabolic reflector antenna to design a planar system which produces the same radiation pattern as the reflector. Both devices are numerically validated. © 2013 IEEE. Source


Sason I.,Technion - Israel Institute of Technology | Shuval B.,Rafael Laboratories
IEEE Transactions on Information Theory | Year: 2011

A design of robust error-correcting codes that achieve reliable communication over various channels is of great theoretical and practical interest. Such codes are termed universal. This paper considers the universality of low-density parity-check (LDPC) code ensembles over families of memoryless binary-input output-symmetric (MBIOS) channels. Universality is considered both under belief-propagation (BP) and maximum-likelihood (ML) decoding. For the BP decoding case, we derive a density-evolution-based analytical method for designing LDPC code ensembles that are universal over various families of MBIOS channels. We also derive a necessary condition for universality of LDPC code ensembles under BP decoding; this condition is used to provide bounds on the universally achievable fraction of capacity. These results enable us to provide conditions for reliable/unreliable communications under BP decoding that are based on the Bhattacharyya parameter of the channel. For the ML decoding case, we prove that properly selected regular LDPC code ensembles are universally capacity-achieving for the set of equi-capacity MBIOS channels and extend this result to punctured regular LDPC code ensembles. © 2011 IEEE. Source

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