Applications of Origami Folding Techniques on Antenna Structures using Flexible Substrates

This thesis investigates the use of Origami folding techniques in antenna structures. This application would be suitable for space satellites and military secure communications. The main research is divided into three segments. The first one presents a Vivaldi antenna using flexible substrates, Kapton and Mylar. They are simulated in Computer Simulation Technology (CST) Studio and tested with a Vector Network Analyser (VNA) in the anechoic chamber. The reason for using various flexible substrates is to determine which substrate would perform better when folded. Each substrate has unique electrical and mechanical properties. Secondly, a more specfic Origami folding pattern called Miura Ori is introduced. It is integrated into two antenna designs: Slot antenna and Substrate Integrated Waveguide (SIW) antenna. The Miura Ori folding technique is a repeated pattern with some interesting mechanical properties. It would be able to switch between different states: at, partially folded or fully folded. This would be beneficial for applications where the cost, size and weight are limited. Both antenna designs are simulated and optimised to achieve a good performance, before incorporating the Miura Ori folding technique. There are special parameters that require the model to be functional, Inner angle and Folding angle. Each antenna is simulated by varying those two parameters, because of that the resonant frequency, reflection coefficient (S11), gain and the direction of the radiating angle is changed. Lastly, a microwave switch with nanowires is investigated to provide a fast switching network at each individual antenna. The microwave switch is simulated on a flexible substrate

Electrochemical Determination of Some Triphenylmethane Dyes by Means of Voltammetry

AbstractThis paper provides the investigation of electrochemical properties of triphenylmethane dyes using a voltammetric method with constant-current potential sweep. Malachite green (MG) and basic fuchsin (BF) have been chosen as representatives of the triphenylmethane dyes. The electrochemical behavior of MG and BF on the surface of a mercury-film electrode depending on рН, the nature of background electrolyte and scan rate of potential sweep have been investigated. The conditions of registration have been determined for MG and BF detecting in the solution. It is demonstrated that the reduction peak currents of MG and BF increase linearly with their concentration in the range of 9.0·10-5- 7.0·10-3 mol/dm3 for MG, 6.0·10-5 – 8.0 10-3 mol/dm3 for BF with correlation coefficients of 0.9987 and 0.9961, respectively. The detection limit of MG is 5.0·10-5 mol/dm3 and for BF - 2.0·10-5 mol/dm3

Implementation of the compulsory universal testing scheme in Hong Kong: Mathematical simulations of a household-based pooling approach

This study aims to propose a pooling approach to simulate the compulsory universal RT-PCR test in Hong Kong and explore the feasibility of implementing the pooling method on a household basis. The mathematical model is initially verified, and then the simulation is performed under different prevalence rates and pooled sizes. The simulated population is based in Hong Kong. The simulation included 10,000,000 swab samples, with a representative distribution of populations in Hong Kong. The samples were grouped into a batch size of 20. If the entire batch is positive, then the group is further divided into an identical group size of 10 for re-testing. Different combinations of mini-group sizes were also investigated. The proposed pooling method was extended to a household basis. A representative from each household is required to perform the RT-PCR test. Results of the simulation replications, indicate a significant reduction (p < 0.001) of 83.62, 64.18, and 48.46% in the testing volume for prevalence rate 1, 3, and 5%, respectively. Combined with the household-based pooling approach, the total number of RT-PCR is 437,304, 956,133, and 1,375,795 for prevalence rates 1, 3, and 5%, respectively. The household-based pooling strategy showed efficiency when the prevalence rates in the population were low. This pooling strategy can rapidly screen people in high-risk groups for COVID-19 infections and quarantine those who test positive, even when time and resources for testing are limited

Promotion of knowledge and awareness of parents in HK about infant oral health care

Aim: To promote the knowledge and awareness of infant oral health (OH) care among Hong Kong parents with children aged 0 to 2 years through an interactive workshop and to evaluate its effectiveness. Methods: Parents were recruited from government-registered childcare centers and private playgroups. Interactive workshops consisted of a 30-minute PowerPoint presentation and 20 minutes of small-group activities, which included infant oral hygiene instruction with custom-made infant dentition models, diet analysis and question-and-answer session. Self-completed questionnaires used to evaluate the knowledge and attitude of parents were distributed before and after the workshops. Scores on general OH knowledge (range=0-18), infant OH knowledge (0-10) and parent’s attitude (0-4) were computed. Scores of at least 70% were considered proficient. Results: Among the 111 participants (aged 26 to 54 years, 64% mothers), 96% had a child aged 0 to 30 months. 30% had their children’s mouth cleaned at least twice a day. Only one participant had brought his/her child to see a dentist. Weaker aspects in parents’ OH knowledge and common misconceptions were identified in the pre-survey. Only 35% identified frequent meals as an increased caries risk; only 59% and 79% identified starchy food and formula milk as cariogenic food respectively. 58% did not know water fluoridation can prevent caries, while 33% of parents pointed out calcium supplement can prevent caries. Before the workshop, 41% had proficient general OH knowledge (mean=11.9) and 16% had proficient infant OH knowledge (mean=4.8). Over half of parents showed positive attitude (mean=3.4). Significant improvements in general OH knowledge (mean=15.6, p<0.001), infant OH knowledge (mean=8.8, p<0.001) and attitude (mean=3.9, p<0.001) were observed. Parents reflected the workshops were useful (94%) and they learned new practices to improve their infants’ OH (95%). Conclusion: Several deficiencies in oral health knowledge and behaviour are identified. The interactive workshops can effectively promote the knowledge and awareness of infant oral health care among parents with children aged 0 to 2 years. Large-scale infant oral health survey is needed. Interactive workshops with longer follow-up periods are recommended. More guidelines can be provided to parents and general dentists for prevention of caries.published_or_final_versio

A Prospective Evaluation of Quick Intraoperative Parathyroid Hormone Assay at the Time of Skin Closure in Predicting Clinically Relevant Hypocalcemia after Thyroidectomy

BACKGROUND: Post-thyroidectomy hypocalcemia is a major contributing factor in delayed hospital discharge and dissuading surgeons from ambulatory thyroidectomy. We prospectively evaluated the accuracy and reliability of quick parathyroid hormone level measurement at skin closure (PTH-SC) in predicting clinically relevant hypocalcemia (i.e., patients requiring calcium +/- calcitriol supplements on hospital discharge). METHODS: Of the 117 patients who underwent a total or completion total thyroidectomy and PTH-SC, 17 (14.5 %) had hypocalcemic symptoms or adjusted calcium 1 pmol/L) had a higher specificity (95.0 %) and AUC (0.887) than serial calcium monitoring or PTH-D1 alone. Although 3/98 of patients with PTH-SC >1 pmol/L required calcium supplements on discharge, they required only the minimum amount to maintain normocalcemia. CONCLUSION: PTH-SC is an accurate and reliable means of predicting clinically relevant hypocalcemia. It would be reasonable to discharge those with PTH-SC >1 pmol/L on the same operative day as the risk of life-threatening hypocalcemia would seem unlikely.published_or_final_versio

Impact of cardiac arrest centers on the survival of patients with nontraumatic out‐of‐hospital cardiac arrest : a systematic review and meta‐analysis

Background The role of cardiac arrest centers (CACs) in out‐of‐hospital cardiac arrest care systems is continuously evolving. Interpretation of existing literature is limited by heterogeneity in CAC characteristics and types of patients transported to CACs. This study assesses the impact of CACs on survival in out‐of‐hospital cardiac arrest according to varying definitions of CAC and prespecified subgroups. Methods and Results Electronic databases were searched from inception to March 9, 2021 for relevant studies. Centers were considered CACs if self‐declared by study authors and capable of relevant interventions. Main outcomes were survival and neurologically favorable survival at hospital discharge or 30 days. Meta‐analyses were performed for adjusted odds ratio (aOR) and crude odds ratios. Thirty‐six studies were analyzed. Survival with favorable neurological outcome significantly improved with treatment at CACs (aOR, 1.85 [95% CI, 1.52–2.26]), even when including high‐volume centers (aOR, 1.50 [95% CI, 1.18–1.91]) or including improved‐care centers (aOR, 2.13 [95% CI, 1.75–2.59]) as CACs. Survival significantly increased with treatment at CACs (aOR, 1.92 [95% CI, 1.59–2.32]), even when including high‐volume centers (aOR, 1.74 [95% CI, 1.38–2.18]) or when including improved‐care centers (aOR, 1.97 [95% CI, 1.71–2.26]) as CACs. The treatment effect was more pronounced among patients with shockable rhythm ( P =0.006) and without prehospital return of spontaneous circulation ( P =0.005). Conclusions were robust to sensitivity analyses, with no publication bias detected. Conclusions Care at CACs was associated with improved survival and neurological outcomes for patients with nontraumatic out‐of‐hospital cardiac arrest regardless of varying CAC definitions. Patients with shockable rhythms and those without prehospital return of spontaneous circulation benefited more from CACs. Evidence for bypassing hospitals or interhospital transfer remains inconclusive

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals &lt;1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Polythiophene and dye blends for the photo-electrocatalytic production of hydrogen

The main finding of this thesis is the discovery of poly(2,2'-bithiophene) (PBTh) as a novel photo-electrocatalyst for the hydrogen evolution reaction (HER). This finding for PBTh is supplemented by studies showing remarkable long term stability, high Faradaic efficiencies, and successful operation over a wide pH range. In-depth mechanistic studies were also conducted and reveal significant insight into the thermodynamic and kinetic mechanism of the PBTh catalyst. The challenge of tackling climate change requires the rapid development of new technologies for sustainable energy use. To this end, hydrogen shows much promise as an alternative for fossil fuels, however, the absence of an efficient H₂ generation method has thus far limited commercial applications. Significant research has been directed towards the development of new catalysts for the HER though none have yet achieved the desired performance requirements. In this study, we utilise the inherent electrochemical and photo-active properties of conducting polymers to tackle this long-standing problem. Initial studies on conducting polymer:dye blends were inspired by earlier research but revealed little catalytic activity. Subsequent in-depth characterisation studies allowed the identification of key issues, whilst revealing promising alternative conducting polymer:dye combinations for further investigation; namely, PBTh and Cresol Red. It was eventually discovered that PBTh displayed photo-electrocatalytic activity towards the HER even without the dye component. As a result, research was redirected to focus on pure PBTh to better understand this novel behaviour. The investigations on PBTh films revealed a range of desirable catalytic properties such as the successful operation in neutral aqueous environments, good stability over 12 days and an onset potential of 0.3 V below E0. The PBTh system also showed significant scope for further improvements which included the threefold increase in the catalytic activity when changing film thickness. This potential for enhancement, together with the inherent desirable catalytic properties, presents PBTh as a particularly exciting photo-electrocatalyst. In the final part of this study, in-depth mechanistic studies were undertaken to elucidate the chemistry behind the catalytic behaviour. Key findings included the exclusion of iron as a possible contaminant, confirmation of the photo-dependence to the optical properties of PBTh and assignment of an equivalent circuit to yield insight into the electrical properties of the PBTh electrode. Most importantly, in-situ Raman spectroscopy analysis was able to reveal the formation of an S-H def. band (at 985 cm-1) which confirmed the proposed intermediate state of a PBTh chain protonated at a sulphur atom (PBTh(S-H)+). Subsequent computational studies supported these findings and revealed promising charge transfer states of the excited PBTh(S-H)+ species. A tentative reaction mechanism is thus put forward, though further experimental data is required to confirm the scheme. The studies presented herein represent the beginnings of the development of PBTh as a photo-electrocatalyst for the HER. These promising initial results have led to the publication of three papers and generated considerable scope for future studies. As it stands, the full potential of the PBTh system has yet to be realised but given the promising performance observed thus far, it is hoped that the eventual optimised system would yield a low-cost and efficient catalyst for the commercial production of H₂

Online learning in management education amid the pandemic: a bibliometric and content analysis

The COVID-19 pandemic (2020–2022) had triggered a global crisis which led to the suspension of colleges and universities. Management educators had digitally transformed their teaching to new modalities with digital technologies and adapted to technological solutions. The management students had experienced different online modes of learning and adjusted their methods to the new reality of content delivery. This study aims to discuss opportunities and challenges for management education and facilitate further investigation into the emerging trends on online learning by analyzing the characteristics of management education research and examining the most frequent research themes from 2020 to 2022. A bibliometric analysis is used to review 920 papers retrieved from the Scopus database for exploring key research themes of management education and online learning. The findings revealed that the publications are concentrated in developed countries while European countries had accounted for the largest proportion of the listed publications. Five sub themes are identified for receiving the most scholarly attention, such as pedagogy, technology, assessment methods, learning outcomes or skills, and challenges. After all, the bibliometric and thematic findings identified pivotal theoretical contributions, including fields of online or blended learning and management education converge, to extend the existing online learning theories