From the zero-field metal-insulator transition in two dimensions to the quantum Hall transition: a percolation-effective-medium theory

Effective-medium theory is applied to the percolation description of the metal-insulator transition in two dimensions with emphasis on the continuous connection between the zero-magnetic-field transition and the quantum Hall transition. In this model the system consists of puddles connected via saddle points, and there is loss of quantum coherence inside the puddles. The effective conductance of the network is calculated using appropriate integration over the distribution of conductances, leading to a determination of the magnetic field dependence of the critical density. Excellent quantitative agreement is obtained with the experimental data, which allows an estimate of the puddle physical parameters

Computational Methods for Stability and Control (COMSAC): The Time Has Come

Powerful computational fluid dynamics (CFD) tools have emerged that appear to offer significant benefits as an adjunct to the experimental methods used by the stability and control community to predict aerodynamic parameters. The decreasing costs for and increasing availability of computing hours are making these applications increasingly viable as time goes on and the cost of computing continues to drop. This paper summarizes the efforts of four organizations to utilize high-end computational fluid dynamics (CFD) tools to address the challenges of the stability and control arena. General motivation and the backdrop for these efforts will be summarized as well as examples of current applications

Performance of Analytic Orbit Propagators on a Hypercube and a Workstation Cluster

In this paper we discuss the benefit of par allel computing in propagating orbits of ob jects. Several analytic methods are now in use operationally . We will discuss three such schemes. We demonstrate the benefit of par allelism by using an INTEL iPSC hyper cube and by using a cluster of Unix based workstations running Parallel Virtual Machine PVM. The software PVM allows a heterogeneous set of networked workstations to appear as a multicomputer. We will show that one can achieve near 100% efficiency on the hypercube