Design considerations for the beam-waveguide retrofit of a ground antenna station

Retrofitting an antenna that was originally designed without a beam waveguide introduces special difficulties because it is desirable to minimize alteration of the original mechanical truss work and to image the actual feed without distortion at the focal point of the dual-shaped reflector. To obtain an acceptable image, certain Geometrical Optics (GO) design criteria are followed as closely as possible. The problems associated with applying these design criteria to a 34-meter dual-shaped DSN (Deep Space Network) antenna are discussed. The use of various diffraction analysis techniques in the design process is also discussed. GTD and FFT algorithms are particularly necessary at the higher frequencies, while Physical Optics and Spherical Wave Expansions proved necessary at the lower frequencies

On Delegation under Relational Contracts

In this paper, a principal’s decision between delegating two tasks or handling one of the two tasks herself is analyzed. We assume that the principal uses both, formal contracts and informal agreements sustained by the value of future relationships (relational contracts) as incentive device. It is found that the principal is less likely to delegate both tasks in a dynamic setting than in a static one (where formal contracts are the only feasible incentive device), as handling one task herself enables a much wider use of relational contracts

On Delegation under Relational Contracts

In this paper, a principal’s decision between delegating two tasks or handling one of the two tasks herself is analyzed. We assume that the principal uses both, formal contracts and informal agreements sustained by the value of future relationships (relational contracts) as incentive device. It is found that the principal is less likely to delegate both tasks in a dynamic setting than in a static one (where formal contracts are the only feasible incentive device), as handling one task herself enables a much wider use of relational contracts.Job design; relational contracts; formal contracts; delegation

Dynamo efficiency with shear in helical turbulence .

To elucidate the influence of shear flow on the generation of magnetic fields through the modification of turbulence property, we consider the case where a large-scale magnetic field is parallel to a large-scale shear flow without direct interaction between the two in the kinematic limit where the magnetic field does not backreact on the velocity. By nonperturbatively incorporating the effect of shear in a helically forced turbulence, we show that turbulence intensity and turbulent transport coefficients (turbulent viscosity, α and β effect) are enhanced by a weak shear, while strongly suppressed for strong shear. In particular, β is shown to be much more strongly suppressed than α effect. We discuss its important implications for dynamo efficiency, i.e., on the scaling of the dynamo number with differential rotation

A characteristic lengthscale causes anomalous size effects and boundary programmability in mechanical metamaterials

The architecture of mechanical metamaterialsis designed to harness geometry, non-linearity and topology to obtain advanced functionalities such as shape morphing, programmability and one-way propagation. While a purely geometric framework successfully captures the physics of small systems under idealized conditions, large systems or heterogeneous driving conditions remain essentially unexplored. Here we uncover strong anomalies in the mechanics of a broad class of metamaterials, such as auxetics, shape-changers or topological insulators: a non-monotonic variation of their stiffness with system size, and the ability of textured boundaries to completely alter their properties. These striking features stem from the competition between rotation-based deformations---relevant for small systems---and ordinary elasticity, and are controlled by a characteristic length scale which is entirely tunable by the architectural details. Our study provides new vistas for designing, controlling and programming the mechanics of metamaterials in the thermodynamic limit.Comment: Main text has 4 pages, 4 figures + Methods and Supplementary Informatio