Attentional abnormalities are one of the earliest signs of Autism Spectrum Disorders (ASD). Despite flourishing attention studies in autism, relatively little is known about attentional performance among young children with high-functioning autism (HFA). The present study compared 23 preschool children with HFA and 28 typically-developing children on attention network efficiencies, selective attention to social or non-social information and attention switching, with age, cognitive and language abilities matched or controlled. Compared with typically-developing children, young children with HFA showed comparative attention network efficiencies, slower orienting to face and better attention switching. Alternative explanations for their strength in attention switching are given based on superior focused attention to visual details and hyper-systemizing skills. Implications on future research and practice are discussed. / published_or_final_version / Educational Psychology / Master / Master of Social Sciences

No description available.

The radio frequency (RF) spectrum is a scarce natural resource, currently regulated by government agencies. With the explosive emergence of wireless applications, the demands for the RF spectrum are constantly increasing. On the other hand, it has been reported that localised temporal and geographic spectrum utilisation efficiency is extremely low. Cognitive radio is an innovative technology designed to improve spectrum utilisation by exploiting those spectrum opportunities. This ability is dependent upon spectrum sensing, which is one of most critical components in a cognitive radio system. A significant challenge is to sense the whole RF spectrum at a particular physical location in a short observation time. Otherwise, performance degrades with longer observation times since the lagging response to spectrum holes implies low spectrum utilisation efficiency. Hence, developing an efficient wideband spectrum sensing technique is prime important. In this thesis, a multirate asynchronous sub-Nyquist sampling (MASS) system that employs multiple low-rate analog-to-digital converters (ADCs) is developed that implements wideband spectrum sensing. The key features of the MASS system are, 1) low implementation complexity, 2) energy-efficiency for sharing spectrum sensing data, and 3) robustness against the lack of time synchronisation. The conditions under which recovery of the full spectrum is unique are presented using compressive sensing (CS) analysis. The MASS system is applied to both centralised and distributed cognitive radio networks. When the spectra of the cognitive radio nodes have a common spectral support, using one low-rate ADC in each cognitive radio node can successfully recover the full spectrum. This is obtained by applying a hybrid matching pursuit (HMP) algorithm - a synthesis of distributed compressive sensing simultaneous orthogonal matching pursuit (DCS-SOMP) and compressive sampling matching pursuit (CoSaMP). Moreover, a multirate spectrum detection (MSD) system is introduced to detect the primary users from a small number of measurements without ever reconstructing the full spectrum. To achieve a better detection performance, a data fusion strategy is developed for combining sensing data from all cognitive radio nodes. Theoretical bounds on detection performance are derived for distributed cognitive radio nodes suffering from additive white Gaussian noise (AWGN), Rayleigh fading, and log-normal fading channels. In conclusion, MASS and MSD both have a low implementation complexity, high energy efficiency, good data compression capability, and are applicable to distributed cognitive radio networks.

The focus of this dissertation is the performance analyses of two classes of frequency-hopped spread-spectrum multiple access (FH-SSMA) systems in various fading environments. The capacity of Viterbi’s FH-SSMA system is evaluated under three types of fading, namely Rician, shadowed Rician, and Nakagami fading. The results of recent experiments have indicated that these fading phenomena occur in various environments where the FH-SSMA system may be implemented. In this dissertation, the deletion probability for each fading scenario is derived. Subsequently, the system capacity is analyzed in terms of maximum number of users versus average bit error rate. The effect of a change in the signal-to-noise ratio level on the system capacity is also demonstrated. For Rician fading, it is found that the capacity of the system with a Rician factor of 2 dB is reduced by 13 percent as compared to the capacity of the non-fading case. For shadowed Rician fading, three shadowing scenarios are considered: light, average, and heavy. It is shown that the light and the average shadowing scenarios provide only a slight decrease in the capacity, while the heavy shadowing scenario renders a capacity identical to that for the Rayleigh fading case. Finally, for Nakagami fading the capacity is found to decrease by 50 percent as the fading parameter is reduced to 0.5. The performance of a cellular frequency-hopped spread-spectrum multiple access system is studied under an indoor environment. It is demonstrated how the system capacity, given in terms of the number of users per cell, is affected by the number of cells in the system. Also, the influence of the delay spread, which is the result of multipath propagation, is investigated. The analysis focuses on a worst-case scenario where a user receives both the desired and interfering signals with equal power levels. This scenario applies to both the downlink and the uplink. It is shown that the system capacity is reduced drastically as the number of adjacent interfering cells increases from one to three. Previous work concerning the indoor multipath propagation assumed that the number of paths is fixed, the path delays are uniformly distributed, and the path gains are equal. In this dissertation, a more realistic channel model derived from actual impulse response measurements by Saleh and Valenzuela is employed. The model consists of clusters of rays with constant cluster and ray arrival rates and power-delay time constants. The system performance is shown to be affected strongly by the change in the power-delay time constants, yet only slightly influenced by the variation in the arrival rates of the rays and clusters. In addition, the degradation in the system performance due to the delay spread becomes more severe as the transmission rate increases. / Graduate

Call number: LD2668 .T4 1950 C64 / Master of Science

We study a dynamic channel selection framework for cognitive radio networks (CRNs) which support both delay sensitive and best effort services. Unlike existing works in the literature, we consider the effect of heterogeneous radio frequency characteristics and heterogeneous primary user activities on channel selection in multi-channel CRNs. Optimal spectrum decision policies are obtained to achieve minimum delay using dynamic programming techniques, such as Markov decision process (MDP) and reinforcement learning, under different assumptions. To address the computational complexity issue in the MDP solutions, a myopic scheme is proposed based on the estimated packet sojourn time. / October 2016

No description available.

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 1996 / In present thesis the results of a study of the combined action of a solid catalyst and a gas-phase inintiator, hydrogen peroxide, in the methane partial oxidation and oxidative coupling reactions are presented. [Abbreviated Abstract. Open document to view full version] / MT2017

by Tsang Kee Kung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1978. / Includes bibliographical references (leaves 99-100).

Autism Spectrum Disorder (ASD) is a pervasive developmental disorder characterized by two distinct features; the social, including impairments in communication and social functioning (empathizing), and the non-social, including preoccupation with restricted interests and repetitive behaviours (systemizing). This thesis investigated non-social cognition in the autism spectrum by undertaking six studies, three with neurotypical participants from the general population and three with an ASD group and matched neurotypical controls. These studies measured autonomic arousal to social and non-social stimuli and stimuli associated with the participant's own special interest or hobby, and change blindness tasks that utilized both social and non-social changes, along with measures of attention to detail and anxiety in an attempt to understand some of the cognitive and affective mechanisms that underlie non-social cognition in ASD and in the wider autism spectrum. A further study assessed 'drive to systemize' along with an objective behavioural assessment of logical thinking ability and a measure of preference for deliberative or intuitive thinking style, to try to further elucidate connections between drive to systemize and ability to systemize, and the modes of cognition that relate to systemizing. Findings included the relationship between autistic traits and stronger physiological responses to non-social stimuli in the neurotypical sample, and a significantly stronger response in the ASD group to non-social stimuli related to personal special interest than in controls. Participants with a larger number of autistic traits showed enhanced change blindness when changes were social in nature. Self-reported high systemizers report that they prefer slow, deliberative styles of thinking and provide more accurate responses to questions that should involve logical thinking-yet they are less able to provide sound logical reasoning for their correct answers than those who are low systemizers. Together, the results suggest that non-social cognition, or systemizing, in autism is motivated by bottom up perceptual and affective processes that share features with conventional social and emotional cognition, or empathizing.