We present results of a grid computer search which enumerated the number of 26-by-26 Costas arrays. Of the 26! possible permutation matrices, only 56 of them satisfy the Costas condition that the N choose 2 line segments connecting pairs of ones are all distinct. The 56 arrays consist of 6 unique non-symmetric arrays which each generate 8 arrays using rotations and reflections and 2 symmetric arrays which each generate 4 arrays using rotations and reflections (56 = 6×8+2×4). This enumeration result shows the falling number of Costas arrays as a function of size continues from its peak at N = 16 to N = 26. As the known generation techniques produce more than 56 arrays for N = 27, N = 26 is the first local minima in the enumeration sequence. The search was performed on 120 machines over a three month period, and thus took nearly 30 years of CPU time. The details of how the search was performed is presented and some observations on the database of known arrays are made.

No abstract

Abstract-This paper presents a newly designed wireless accelerometer-based movement measurement device. The device is capable of measuring activity ranging from gross body movements to more subtle vibrations emanating from the body, including laryngeal vibration and the mechanomyogram (mechanical vibrations from working muscles). The main body of the device, which is less than 20cm 3 in volume and weighs less than 50g, contains a microcontroller, wireless transceiver, battery, and one accelerometer. A supplementary accelerometer module is connected to the main device by thin wires. This module is very light weight and can therefore be directly attached to the skin to measure laryngeal vibration, mechanomyogram, or cardiac muscle movement.The prototype device has been initially applied to facilitating play and creative expression by children with physical disabilities. For this purpose, the main module was adapted to be worn behind the ear while the supplementary accelerometer module is attached to the skin over the larynx.In this paper, the device has been adapted to allow guidance of a radio controlled toy car. Direction is controlled by tilting the head, as measured by the accelerometer in the main device. The supplementary accelerometer is used to measure vocal pitch which controls the car's speed. The device has also been adapted to control a music synthesizer, with frequency of phonation controlling musical pitch while head position, which is measured by the main device's accelerometer, controls another parameter such as timbre.Preliminary user trials with five subjects were carried out in these two applications and the results are presented. The system is also readily amenable to adaptation for other applications such as wheelchair navigation, mouse pointer control, or computer game input.

Gate drive circuits for power mosfets Advances in recent years in the manufacture of metal oxide Field Effect Transistors (Mosfets) have paved the way for new design criteria in solid-state switching power circuits. This paper gives an insight into the knowledge gained in the design of gate drive circuits for power mosfet switching devices.