N-particle dynamics of the Euler equations for planar diffeomorphisms

The Euler equations associated with diffeomorphism groups have received much recent study because of their links with fluid dynamics, computer vision, and mechanics. In this article, we consider the dynamics of N point particles or “blobs” moving under the action of the Euler equations associated with the group of diffeomorphisms of the plane in a variety of different metrics. This dynamical system is already in widespread use in the field of image registration, where the point particles correspond to image landmarks, but its dynamical behavior has not previously been studied. The 2-body problem is always integrable, and we analyze its phase portrait under different metrics. In particular, we show that 2-body capturing orbits (in which the distances between the particles tend to 0 as t  → ∞) can occur when the kernel is sufficiently smooth and the relative initial velocity of the particles is sufficiently large. We compute the dynamics of these “dipoles” with respect to other test particles, and supplement the calculations with simulations for larger N that illustrate the different regimes.     

Armoured Selection Decision Support Software

ABSTRACT

Selecting a main battle tank for an army is a lengthy and complex decision-making process. Military procurement staffs use various management and engineering tools to conduct their studies. This article describes a decision support software package that can assist in selecting the best tank from a set of competitors. The package assesses the design features that affect three major performance criteria: firepower, protection, and mobility. The package combines the Expert Choice^? implementation of the analytical hierarchy process with a LOTUS^? spreadsheet.     

Fast, On-Line Learning of Globally Consistent Maps

To navigate in unknown environments, mobile robots require the ability to build their own maps. A major problem for robot map building is that odometry-based dead reckoning cannot be used to assign accurate global position information to a map because of cumulative drift errors. This paper introduces a fast, on-line algorithm for learning geometrically consistent maps using only local metric information. The algorithm works by using a relaxation technique to minimize an energy function over many small steps. The approach differs from previous work in that it is computationally cheap, easy to implement and is proven to converge to a globally optimal solution. Experiments are presented in which large, complex environments were successfully mapped by a real robot.     

Millimetre-wave second harmonic generation on a nonlinear transmission line

Phase-matching between two forward waves on a monolithic nonlinear transmission line is achieved by alternating the length of the interconnecting transmission lines. With an input of 20 dBm at 50 GHz, amplitudes up to 1 V at 100 GHz have been measured by direct electro-optic sampling.<>     

Lucky drift estimation of excess noise factor for conventionalavalanche photodiodes including the dead space effect

A technique for estimating the excess noise factor in conventional avalanche photodiodes has been developed. It is based upon a computer simulation of carrier motion using the lucky drift concept. The importance of the impact ionization dead space is demonstrated, and an established theory is shown to overestimate the excess noise factor due to the neglect of the dead space phenomenon in conventional avalanche photodiodes     

Improved transmit steering for MIMO-OFDM downlinks with distributed base station antenna arrays

Space-division multiple-access (SDMA) is a communication technique that enables a base station to communicate with several mobile users simultaneously. The ability of the base station to spatially separate several users depends on the pairwise cross correlations between the channel matrices of the users (the inter-user correlation). In this paper, we propose an improved steering downlink multiple-input-multiple-output-orthogonal frequency-division multiplexing (OFDM) system that reduces both the inter-user correlation and the near-far problem resulting in a significant enhancement in system performance. In this system, several base station multiantenna arrays are distributed in a given area. Each array communicates with the base station via optical fiber links, and all transmitter signal processing is performed at the base station. Multiantenna users are spatially separated such that only a subset of the users is served by each tone of the OFDM symbol. The served users are selected based on an algorithm that reduces the inter-user correlations. Distributing the arrays around the users also balances the channel matrix leading to significant reduction in the effect of the near-far problem. The channel matrix of each user is assumed correlated and Ricean distributed. Several data symbols can be spatially multiplexed to each user over each OFDM tone with high reliability and with good total system capacity.     

Differential detection of turbo codes for Rayleigh fast-fadingchannels

The performance of turbo codes using differentially detected quadrature phase-shift keying (QPSK) signals transmitted over Rayleigh fast-fading channels is investigated. So far in the open technical literature dealing with turbo codes only slow fading has been considered. Our research has shown that the use of a simple differential detector in conjunction with turbo codes can generally outperform convolutional codes in terms of the bit-and block-error rates for fading rates with a BT product up to 0.1. However, to achieve significant performance improvements, large block sizes must be employed, particularly at slower fading rates     

Generation of 3.5-ps fall-time shock waves on a monolithic GaAsnonlinear transmission line

It is shown that nonlinear wave propagation on a monolithic GaAs nonlinear transmission line can form shock waves with fall time as short as 3.5 ps. An output fall time of 4.3 ps was measured for a single line driven at 15 GHz (20-ps fall time) while a cascade of two lines driven at 8 GHz (37-ps fall time) produced a 2-V wavefront with 3.5-ps fall time     

Scattering from an open spherical shell having a circular apertureand enclosing a concentric dielectric sphere

The generalized dual series solution is presented for the scattering of an arbitrary plane wave from an open spherical shell having a circular aperture and enclosing a concentric homogeneous dielectric sphere. This solution explicitly exhibits the correct edge behavior, and it can handle spheres that are electrically small or large without special considerations. A variety of cross-section results is presented for the normally incident case. It is shown that effects corresponding to the presence of the interior cavity dominate all of the scattering data. In particular, the cross sections exhibit new resonance features that are due to the cavity-backed nature of the aperture and depend on the characteristics of the interior sphere. The results demonstrate that interior information is contained in the exterior scattering data     

A heterogeneous dual processor

Details of a computer-computer communication facility are presented. The primary feature of the system is the use of a single terminal to monitor and control processes on different machines simultaneously, working together on the solution of a common problem. Experience with an application, error handling and maintenance of synchronization are described.