Charles P. Unsworth

A robust sequence synchronization unit for multi-user DS-CDMA chaos-based communication systems

This paper demonstrates a way of achieving and maintaining sequence synchronization in multi-user direct sequence code division multiple access (DS-CDMA) based chaotic communication systems. Synchronization is achieved and maintained through the code acquisition and the code tracking phase, respectively. The performance of the proposed system is evaluated in the presence of additive white Gaussian noise and interuser interferences. Throughout, a pseudo-random binary sequence (PRBS) is used as the synchronizing pilot signal within the multi-user chaotic communication system. In addition, the Logistic and Bernoulli chaotic maps are also used as the pilot signals in the investigation of the code acquisition performance. The code acquisition circuit is evaluated in terms of the probability of detection and probability of false alarm. The corresponding results demonstrate an ability to achieve initial synchronization. Furthermore, it is shown that in terms of code acquisition, the PRBS outperforms the Logistic and Bernoulli chaotic maps. A mathematical model of the code tracking loop is then presented. From the model, a control law for the generation of time offset estimates is derived. The robustness of the synchronization unit is then demonstrated in terms of the bit error rate. It has been shown that for the case of 1, 2, 3, 4, and 5 users, the bit error rate goes below the maximum acceptable limit of 10^-^3 at the bit energy to noise power spectral density ratio of approximately 8, 9, 9.5, 11, and 12dB, respectively. Furthermore, a gradual degradation in performance, above the maximum acceptable bit error rate limit, is demonstrated for the increasing number of users.

Application of xCELLigence RTCA Biosensor Technology for Revealing the Profile and Window of Drug Responsiveness in Real Time

The xCELLigence technology is a real-time cellular biosensor, which measures the net adhesion of cells to high-density gold electrode arrays printed on custom-designed E-plates. The strength of cellular adhesion is influenced by a myriad of factors that include cell type, cell viability, growth, migration, spreading and proliferation. We therefore hypothesised that xCELLigence biosensor technology would provide a valuable platform for the measurement of drug responses in a multitude of different experimental, clinical or pharmacological contexts. In this manuscript, we demonstrate how xCELLigence technology has been invaluable in the identification of (1) not only if cells respond to a particular drug, but (2) the window of drug responsiveness. The latter aspect is often left to educated guess work in classical end-point assays, whereas biosensor technology reveals the temporal profile of the response in real time, which enables both acute responses and longer term responses to be profiled within the same assay. In our experience, the xCELLigence biosensor technology is suitable for highly targeted drug assessment and also low to medium throughput drug screening, which produces high content temporal data in real time.

Patterning and detailed study of human hNT astrocytes on parylene-C/silicon dioxide substrates to the single cell level

It is estimated that the adult human brain contains 100 billion neurons with 5-10 times as many astrocytes. Although it has been generally considered that the astrocyte is a simple supportive cell to the neuron, recent research has revealed new functionality of the astrocyte in the form of information transfer to neurons of the brain. In our previous work we developed a protocol to pattern the hNT neuron (derived from the human teratocarcinoma cell line (hNT)) on parylene-C/SiO(2) substrates. In this work, we report how we have managed to pattern hNT astrocytes, on parylene-C/SiO(2) substrates to single cell resolution. This article disseminates the nanofabrication and cell culturing steps necessary for the patterning of such cells. In addition, it reports the necessary strip lengths and strip width dimensions of parylene-C that encourage high degrees of cellular coverage and single cell isolation for this cell type. The significance in patterning the hNT astrocyte on silicon chip is that it will help enable single cell and network studies into the undiscovered functionality of this interesting cell, thus, contributing to closer pathological studies of the human brain.

First human hNT neurons patterned on parylene-C/silicon dioxide substrates: Combining an accessible cell line and robust patterning technology for the study of the pathological adult human brain

In this communication, we describe a new method which has enabled the first patterning of human neurons (derived from the human teratocarcinoma cell line (hNT)) on parylene-C/silicon dioxide substrates. We reveal the details of the nanofabrication processes, cell differentiation and culturing protocols necessary to successfully pattern hNT neurons which are each key aspects of this new method. The benefits in patterning human neurons on silicon chip using an accessible cell line and robust patterning technology are of widespread value. Thus, using a combined technology such as this will facilitate the detailed study of the pathological human brain at both the single cell and network level.

Chaos-based multi-user time division multiplexing communication system

A chaos-based multi-user time division multiplexing (TDM) communication system has been proposed and its benchmark performance compared to that of the chaos-based direct sequence code division multiple access (DS-CDMA) system in the noisy and Rayleigh fading channels. The benchmark performance of the systems is investigated in terms of the bit error rate (BER) under the assumption of perfect synchronisation. The chaotic spreading signals, used to encrypt the binary messages, are generated using the logistic map. The degradation in performance of the systems in the Rayleigh fading channel when compared with the noisy channel is demonstrated. Furthermore, it is shown that in both noisy and Rayleigh fading channels, the chaos-based multi-user TDM system outperforms the chaos-based DS-CDMA system for a large number of users in the system, whereas the chaos-based DS-CDMA system yields better performance for low user numbers. The overall BER performance degradation for the chaos-based DS-CDMA multi-user system in noisy and Rayleigh fading channels is characterised by the flattening of the BER curves at low levels of noise due to the prevailing effects of the interuser interferences.

A Detailed Noise Characterization and Sensor Evaluation of the North Island of New Zealand Using the PQLX Data Quality Control System

In this paper we analyze five years of recordings (2005-2009) from the National Seismograph Network in the North Island of New Zealand using the power spectral density probability density function (PDF) method of McNamara and Buland (2004). At each station the ambient noise is characterized and the stable noise model is then represented with the modes of the corresponding PDFs over all periods. Obtaining such an accurate long-term noise baseline for each station provides a reference model that should serve to prioritize maintenance issues for the network operators. The PDF mode low-noise model (MLNM) for the North Island is then obtained from the minimum of all the noise modes at each period. The maximum and minimum differences between the North Island MLNM and the noise mode model periods are then calculated at each station as a quick assessment tool. The daily and seasonal variations of the noise mode model are then characterized, and the horizontal and vertical mode noise models are then compared at each station. The applied tech- nique is practical for evaluating the cultural noise condition and the earthquake detec- tion capability, as well as the installation design against unwanted tilt and temperature variation.

Excessive Noise Injection Training of Neural Networks for Markerless Tracking in Obscured and Segmented Environments

In this letter, we demonstrate that the generalization properties of a neural network (NN) can be extended to encompass objects that obscure or segment the original image in its foreground or background. We achieve this by piloting an extension of the noise injection training technique, which we term excessive noise injection (ENI), on a simple feedforward multilayer perceptron (MLP) network with vanilla backward error propagation to achieve this aim. Six tests are reported that show the ability of an NN to distinguish six similar states of motion of a simplified human figure that has become obscured by moving vertical and horizontal bars and random blocks for different levels of obscuration. Four more extensive tests are then reported to determine the bounds of the technique. The results from the ENI network were compared to results from the same NN trained on clean states only. The results pilot strong evidence that it is possible to track a human subject behind objects using this technique, and thus this technique lends itself to a real-time markerless tracking system from a single video stream.

Enrichment of differentiated hNT neurons and subsequent analysis using flow-cytometry and xCELLigence sensing.

BACKGROUND Human neurons (hNT neurons), obtained from the NTera2/D1 precursor cell line, are highly valued by many neuroscientists as isolation of adult human primary neuronal cells continues to elude us. hNT neurons are generated by differentiation of the NT2 precursors for a period of 4 weeks followed by 2 weeks of mitotic inhibition. This yields a heterogeneous population of neuronal phenotypes and underlying astrocyte precursors, the latter of which are very difficult to visualise using standard light microscopy. Such a mixed culture is acceptable for some applications (e.g. measurement of synaptic plasticity), whereas others (e.g. proteomics or transcriptomics) require almost pure cultures of hNT neurons. NEW METHOD Here we describe a simple method for obtaining highly enriched cultures of hNT neurons following the first neuronal harvest and detail several additional methods, namely flow-cytometry and xCELLigence© biosensor technology, to rapidly and reliably determine the purity and viability of the cultures. COMPARISON WITH EXISTING METHODS This method of enrichment for the neurons is novel and advances the end user applications of the cells. RESULTS In addition, we apply the enrichment method to conduct analysis of cell-surface markers using flow-cytometry on the enriched neuronal cells. Furthermore, we apply this method to generate enriched neuronal cells on which we conduct analysis of cell-surface markers using flow-cytometry. CONCLUSIONS Collectively, this paper describes several new advances, which will create opportunities when using these cells and similar preparations, and provides the protocol for analysis of these cells using flow-cytometry and biosensor technology.

Route, speed and mode of oak postglacial colonisation across the British Isles: Integrating molecular ecology, palaeoecology and modelling approaches

Summary This paper describes the route, speed and mode of colonisation of oaks by integrating a number of independent analyses using molecular ecology, palaeoecology and simulation modelling approaches. Using a synthetic map of the contemporary distribution of chloroplast DNA (integrating several published and unpublished data sets and describing variation in 1468 trees from 313 autochthonous stands of Q. robur and Q. petraea from Britain and Ireland), and considering the postglacial topographic landscape, the most likely routes of postglacial colonisation across the British Isles are suggested. The overall pattern of these directions agrees with previous interpretations, but several routes, particularly those into Ireland, differ from previous interpretations and benefit here from using a single synthesised data set. Interestingly, the Atlantic oakwoods appear to have been colonised by individuals bearing a single haplotype (type 12). Two palaeoecology data sets, published separately for Britain and Ireland, are synthesised here and used to infer the timing of first arrival of oaks across the British Isles (between 9500 and 6000 years before present). The maximum observed colonisation speed within the British Isles is approximately 500 m year-1 in central and southern England. Outputs from a simulation model, which mimics postglacial colonisation processes, and which has been parameterised for the colonisation rate observed from the pollen core record and contemporary cpDNA structure, predict that the rapid colonisation rate observed, for at least the southern portion of the British Isles, can only be achieved via very rare (an approximate frequency 0.01%), very long distance seed dispersal events (up to 100 km). Potential agents of such dispersal events are birdsor major meteorological disturbances, e.g. hurricanes. Additional simulation modelling and genetic analysis of latitudinally stratified populations indicate that non-synchronous colonisation fronts, topographic barriers and temperature related survival may also have had an effect on the speed of migration and resulting genetic structure. Finally, in an attempt to record predicted long distance seed dispersal events, a novel curve fitting technique is applied to molecular parentage assignment data for field established seedlings from a contemporary population. A notable discrepancy is recorded between contemporary field estimates (just over 1 km) and those predicted by simulation modelling, and is discussed in detail. A concluding section describes future research priorities.

Superiority of high frequency hypoxic ischemic EEG signals of fetal sheep for sharp wave detection using Wavelet-Type 2 Fuzzy classifiers

There is approximately a 6-8 hour window that exists from when a hypoxic-ischemic insult occurs, in utero, before significant irreversible brain injury occurs in new born infants. The focus of our work is to determine through the electroencephalogram (EEG) if such a hypoxic-ischemic insult has occurred such that neuro-protective treatment can be sought within this period. At present, there are no defined biomarkers in the EEG that are currently being used to help classify if a hypoxic ischemia insult has occurred. However, micro-scale transients in the form of spikes, sharps and slow waves exists that could provide precursory information whether a hypoxic-ischemic insult has occurred or not. In our previous studies we have successfully automatically identified spikes with high sensitivity and selectivity in the conventional 64Hz sampled EEG. This paper details the significant advantage that can be obtained in using high frequency 1024Hz sampled EEG for sharp wave detection over the typically employed 64Hz sampled EEG. This advantage is amplified when a combination of wavelet Type-2 Fuzzy Logic System (WT-Type-2-FLS) classifiers are used to identify the sharp wave transients. By applying WT-Type-2-FLS to the 1024Hz EEG record and to the same down-sampled 64Hz EEG record we demonstrate, how the sharp wave transients detection increases significantly for high resolution 1024Hz EEG over 64Hz EEG. The WT-Type-2-FLS algorithm performance was assessed over 3 standardised time periods within the first 8 hours, post occlusion of a fetal sheep, in utero. 1024Hz EEG results demonstrate the algorithm detected sharps with overall performance rates of 85%, 92%, and 87% in the Early/Mid and Late-latent phases of injury, respectively as compared to 25%, 55% and 31% in the 64Hz EEG. These results demonstrate the power of Wavelet Type-2 Fuzzy Logic System at detecting sharp waves in 1024Hz EEG and suggest that there should be a movement toward recording high frequency EEG for analysis of hypoxic ischemic micro-scale transients that does not occur at present.