Phil Picton

This paper addresses the problem of identifying the chemical species present in a plasma using optical emission spectra. Two neural networks are initially explored, a multilayer perceptron and a linear associative memory which is trained using the Penrose pseudoinverse matrix. However, examination of the spectra leads to a proposal of a more appropriate architecture in which individual neurons are trained on individual species.

This paper presents a performance evaluation of intercell interference and packets collision in scalable Low Power Wide Area Networks (LPWANs). The collision problem is one of the most critical challenges in LPWANs because it can substantially affect network performance and reliability. The paper also offers a rigorous and flexible mathematical model for the ALOHA-based random access protocol with the support of multiple groups of devices and multiple message copies. The analysis is based on the worst-case scenario of message collision, which calculates the message lost ratio (MLR) by assuming that even a weak overlap between two packets in the time-frequency domain leads to the loss of both. Simulations of Weightless-N and Sigfox LPWAN technologies using a variable number of devices, message copies, payload, transmission time, and channels offer some fresh insights into the LPWANs performance. For example, increasing the number message copies reduces the MLR but only up to a certain number of connected devices. After which, the redundancy in packet transmission is no longer beneficial.

There are different techniques used by Machine- to-machine (M2M) communications technologies to mitigate collision problem and data loss. One of these techniques is Frequency Hopping (FH), which is used by Weightless-N technology with a special random channel selection algorithm. In such a system, the probability of a message collision mainly depends on the randomisation algorithm used to access channels. This paper provides a novel randomisation algorithm for the channel selection process of the Weightless-N system. The new proposed algorithm is based on a uniform randomization distribution and called a Uniform Randomisation Channel Selection Technique (URCST). This new algorithm provides a better system performance and lower probability of collision. In addition, it is faster and easier than the Mersenne Twister algorithm.

A recent paper and patent claims to have found a method of finding a threshold logic solution for all linearly separable Boolean functions. Although the method appears to work, one step of the method has not previously been proven. This paper gives a proof that the method does work.

The aim of this paper is to investigate the effect of time delays on the stability of a zero-placement position and velocity feedback law for a vibratory system comprising harmonic excitation equipped with an electromagnetic active tuned mass damper (ATMD). The purpose of the active control is broadening the vibration attenuation envelope of a primary mass to a higher frequency region identified as from 50±0.5Hz with a passive tuned mass damper (TMD) to a wider range of 50±5Hz with an ATMD. Stability conditions of the closed-loop system are determined by studying the position of the system closed-loop poles after the introduction of time delays for different excitation frequencies. A computer simulation of the model predicted that the proposed control system is subject to instability after a critical time delay margin dependent upon the frequency of excitation and the finding were experimentally validated. Three solutions are derived and experimentally tested for minimising the effect of time delays on the stability of the control system. The first solution is associated with the introduction of more damping in the absorber system. The second incorporates using a time-delayed ATMD by tuning its original natural resonant frequency to beyond the nominal operational frequency range of the composite system. The third involves an online gain tuning of filter coefficients in a dual arrangement of low-pass and high-pass filters to eliminate the effect time delays by manipulating the signal phase shifts.