Chemical characterization of chitin from New Zealand plants and their use as digestive aids : A dissertation submitted in partial fulfilment of the requirements for the Degree of Master of Science at Lincoln University

Natural polysaccharide, Chitin is a biopolymer isolated from shells and exoskeletons of fungal, algal, insect, molluscs and crustacean sources, and the extraction method varies among different sources. Among all these sources, crustaceans produce millions of tonnes of this polysaccharide every year, and are discharged in the form of snow in the sea floor, causing harm to the marine ecosystem. Known for their biocompatible, biodegradable and non-toxic nature, chitin and its monomers finds significant role in different sectors of economy. Even though, extraction of chitin from marine sources increases their economic value, one important factor, which is limiting this process, is the inconsistency in raw material supply annually and variability in physicochemical characteristics, owing to difference of process conditions. To overcome these problems and to develop clean labeled chitin polymers, alternative sources could be considered which offers consistent production. This work hence focuses on extraction of chitin from leaves of New Zealand plant- Phormium tenax, using Agaricus bisporus mushroom as positive control. Leaves were considered, as seeds of the same plant gave comparable results to standard chitin extraction, when carried out previously at Lincoln University. Leaves of Phormium tenax are known for their known fibre content and exhibits properties and applications similar to chitin. The leaf fibres are used by Maori community mainly for wound healing, and textile applications and are an important part of New Zealand bio-diversity. The fibre Approximately 37 g/100g and 38 g/100g of Chitin are obtained respectively from Agaricus bisporus (positive control) and pure chitin (standard chemical) after extraction, as quantified by HPLC-FLP method. Overall, the recovery is comparatively low, hence disproving the hypothesis that this extraction method works successfully in extracting chitin from all sources. Also, the chitin recovered from Phormium tenax leaf is non-quantifiable comparing to mushrooms and pure chitin, hence indicating the chance of some complex interaction between chitin and other bioactive components present in leaves. The last part of the study was the development of a fermented functional beverage, kefir and study of its physico-chemical properties. 5 different formulations of kefir (4 with milk as base and 1 with carrot juice as base); with roasted and un-roasted white and brown button mushrooms (Agaricus bisporus) were considered to study if mushrooms had a stabilization effect on kefir. The results of viscosity and pH clearly indicate that roasted white mushrooms offers a stabilization effect on kefir, compared to unroasted and roasted brown mushrooms. However no significant results were obtained in TSS and syneresis studies

Joint Power-control and Antenna Selection in User-Centric Cell-Free Systems with Mixed Resolution ADC

In this paper, we propose a scheme for the joint optimization of the user transmit power and the antenna selection at the access points (AP)s of a user-centric cell-free massive multiple-input-multiple-output (UC CF-mMIMO) system. We derive an approximate expression for the achievable uplink rate of the users in a UC CF-mMIMO system in the presence of a mixed analog-to-digital converter (ADC) resolution profile at the APs. Using the derived approximation, we propose to maximize the uplink sum-rate of UC CF-mMIMO systems subject to energy constraints at the APs. An alternating-optimization solution is proposed using binary particle swarm optimization (BPSO) and successive convex approximation (SCA). We also propose a complete meta-heuristic-based solution that can be used as an alternative solution for applications where latency is the critical metric. Along with this, we used a genetic algorithm (GA)-based approach to compare the performance of the proposed algorithm. We study the impact of various system parameters on the performance of the system

Instantaneous Channel Oblivious Phase Shift Design for an IRS-Assisted SIMO System with Quantized Phase Shift

We design the phase shifts of an intelligent reflecting surface (IRS)-assisted single-input-multiple-output communication system to minimize the outage probability (OP) and to maximize the ergodic rate. Our phase shifts design uses only statistical channel state information since these depend only on the large-scale fading coefficients; the obtained phase shift design remains valid for a longer time frame. We further assume that one has access to only quantized phase values. The closed-form expressions for OP and ergodic rate are derived for the considered system. Next, two optimization problems are formulated to choose the phase shifts of IRS such that (i) OP is minimized and (ii) the ergodic rate is maximized. We used the multi-valued particle swarm optimization (MPSO) and particle swarm optimization (PSO) algorithms to solve the optimization problems. Numerical simulations are performed to study the impact of various parameters on the OP and ergodic rate. We also discuss signaling overhead between BS and IRS controller. It is shown that the overhead can be reduced up to $99.69 \%$ by using statistical CSI for phase shift design and $5$ bits to represent the phase shifts without significantly compromising on the performance

Joint Power-control and Antenna Selection in User-Centric Cell-Free Systems with Mixed Resolution ADC

In this paper, we propose a scheme for the joint optimization of the user transmit power and the antenna selection at the access points (AP)s of a user-centric cell-free massive multiple-input-multiple-output (UC CF-mMIMO) system. We derive an approximate expression for the achievable uplink rate of the users in a UC CF-mMIMO system in the presence of a mixed analog-to-digital converter (ADC) resolution profile at the APs. Using the derived approximation, we propose to maximize the uplink sum rate of UC CF-mMIMO systems subject to energy constraints at the APs. An alternating-optimization solution is proposed using binary particle swarm optimization (BPSO) and successive convex approximation (SCA). We also study the impact of various system parameters on the performance of the system