2,696 research outputs found

    Wireless transmission protocols using relays for broadcast and information exchange channels

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    Relays have been used to overcome existing network performance bottlenecks in meeting the growing demand for large bandwidth and high quality of service (QoS) in wireless networks. This thesis proposes several wireless transmission protocols using relays in practical multi-user broadcast and information exchange channels. The main theme is to demonstrate that efficient use of relays provides an additional dimension to improve reliability, throughput, power efficiency and secrecy. First, a spectrally efficient cooperative transmission protocol is proposed for the multiple-input and singleoutput (MISO) broadcast channel to improve the reliability of wireless transmission. The proposed protocol mitigates co-channel interference and provides another dimension to improve the diversity gain. Analytical and simulation results show that outage probability and the diversity and multiplexing tradeoff of the proposed cooperative protocol outperforms the non-cooperative scheme. Second, a two-way relaying protocol is proposed for the multi-pair, two-way relaying channel to improve the throughput and reliability. The proposed protocol enables both the users and the relay to participate in interference cancellation. Several beamforming schemes are proposed for the multi-antenna relay. Analytical and simulation results reveal that the proposed protocol delivers significant improvements in ergodic capacity, outage probability and the diversity and multiplexing tradeoff if compared to existing schemes. Third, a joint beamforming and power management scheme is proposed for multiple-input and multiple-output (MIMO) two-way relaying channel to improve the sum-rate. Network power allocation and power control optimisation problems are formulated and solved using convex optimisation techniques. Simulation results verify that the proposed scheme delivers better sum-rate or consumes lower power when compared to existing schemes. Fourth, two-way secrecy schemes which combine one-time pad and wiretap coding are proposed for the scalar broadcast channel to improve secrecy rate. The proposed schemes utilise the channel reciprocity and employ relays to forward secret messages. Analytical and simulation results reveal that the proposed schemes are able to achieve positive secrecy rates even when the number of users is large. All of these new wireless transmission protocols help to realise better throughput, reliability, power efficiency and secrecy for wireless broadcast and information exchange channels through the efficient use of relays

    In-Column Electrochemical Detection for Liquid Chromatography

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    This research focuses on the development of whole column detection (WCD) for liquid chromatography (LC). The WCD uses electrochemical techniques for detecting the analytes passing through the separation column. Electrode array for in-column electrochemical detection (ICED) is fabricated along the separation column to enable whole column separation monitoring and allow better understanding on the affinity of particular analyte to the stationary and mobile phases. Numerical models were built to understand the feasibility and differences of electrochemical detection within an unpacked and packed column. From the simulated results, the surface area of the electrode was not hindered by the presence of the particles in flow condition. An electrochemical microfluidic device has been successfully fabricated on PET (polyethylene terephthalate) substrate using the reverse imprinting technique. The photolithographically produced gold metal electrode lines were imprinted into the PET substrate using a blank mould and produced an inlaid electrode array with overall step residue within 40 nm. The semi-cured thermoset polyester channel was irreversibly thermal bonded on the PET substrate. The devices were able to tolerate pressure in excess of 90 bars. The PET column was packed with 5 μm C18 silica beads to perform reverse phase chromatography separation. The array was electrochemically characterised using standard redox probes in both stagnant conditions and under flow. Both numerical modelling and experimental data show improved sensitivity under flow and a limiting current which scaled linearly with cubic root of volume flow rate. Isocratic and gradient mode chromatographic separations of neurotransmitters and metabolites: serotonin, dopamine, adrenaline, 5- HIAA and DOPAC were conducted in the fabricated device. Separation progress was electrochemically detected at multiple locations along the column. Whole column assessment on separation efficiency and column packing efficiency monitoring were conducted using the ICED

    WCF processing in the L2 curriculum: A look at type of WCF, type of linguistic item, and L2 performance

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    Whether type of written corrective feedback (WCF) impacts L2 learning has been investigated for decades. While many product-oriented studies report conflicting findings, the paucity of studies adopting both a process-oriented and curricular approach (e.g., Caras, 2019) underscores the call for further research on: a) the processing dimension of L2 writers’ engagement with WCF in this instructed setting (Manchón & Leow, 2020), b) from an ISLA applied perspective (Leow, 2019a; Leow & Manchón, 2022), and c) any potential relationship with subsequent performances. Also, whether type of linguistic item (e.g., morphological vs. syntactic) plays a role in the processing dimension also warrants further probing. This preliminary quasi-experimental study explored the cognitive processes of 10 adult L2 writers with minimal previous exposure to Spanish interacting with WCF (both direct and metalinguistic) on morphological and syntactic errors. Think aloud data gathered from three compositions written within the natural writing conditions of a foreign language curriculum were transcribed, coded for depth of processing (DoP) (Leow, 2015), and correlated with subsequent performances on the target items. The results revealed: 1) a higher DoP for metalinguistic WCF, 2) differences in processing of linguistic items, 3) similar DoP over time, and 4) a beneficial relationship between DoP and subsequent performances. Recommendations for future research underscore the importance of acknowledging variables within the instructed setting that may impact a pure effect of WCF on L2 development

    Flow velocity mapping using contrast enhanced high-frame-rate plane wave ultrasound and image tracking: methods and initial in vitro and in vivo evaluation

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    Ultrasound imaging is the most widely used method for visualising and quantifying blood flow in medical practice, but existing techniques have various limitations in terms of imaging sensitivity, field of view, flow angle dependence, and imaging depth. In this study, we developed an ultrasound imaging velocimetry approach capable of visualising and quantifying dynamic flow, by combining high-frame-rate plane wave ultrasound imaging, microbubble contrast agents, pulse inversion contrast imaging and speckle image tracking algorithms. The system was initially evaluated in vitro on both straight and carotid-mimicking vessels with steady and pulsatile flows and in vivo in the rabbit aorta. Colour and spectral Doppler measurements were also made. Initial flow mapping results were compared with theoretical prediction and reference Doppler measurements and indicate the potential of the new system as a highly sensitive, accurate, angle-independent and full field-of-view velocity mapping tool capable of tracking and quantifying fast and dynamic flows

    Assessing Malaysia’s Manufactured Exports Competitiveness In The East Asian Region: A Shift-Share And Simulation Approach.

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    Bagi kebanyakan negara Asia Timur, perdagangan antarabangsa menyumbangkan sebahagian besar daripada Keluaran Dalam Negeri Kasar (KDNK) dan kepentingannya kian meningkat. For most East Asian countries, international trade represents a significant portion of their Gross Domestic Product (GDP). Albeit on a different scope and scale, the importance of international trade is rising over the years
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