| Author |
Cui, Jia |
| Title |
Supporting product innovation using 3D shape grammars within a generative design framework |
| Department | School of Design |
| Year | 2015 |
| Subject |
Computer-aided design. Hong Kong Polytechnic University -- Dissertations |
| Degree | Ph.D. |
| Pages | xv, 236 pages : color illustrations |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2828995 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/8277 |
| Abstract |
In the high-tech period,the mix of information prevails every area.Design is a long-history subject mainly relies on designers' experiences, inspirations and aesthetic evaluations. Computer technologies involve in design process to support auxiliary assistances for designers and release them from some tedious time- and labor- consuming tasks, which named as Computer-aided Design (CAD). Collaborating with AI-based approaches (generic programming, evolutionary computation and generative strategy),design automation becomes promising in CAD area instead of being a tool merely. Advanced interactions between design and automatic system can be helpful to notice the intangible design information which belongs to the subjective area in design, now controlled by designers unintentionally. In this study, it puts efforts to enhance the communications between design- and technology- end. From shape representation, design process representation and design evaluation, design information can be recorded and used to build a generative environment for novel design solutions' exploration. It introduces a novel dynamic shape representationthe DSR shape, a 3D design grammarthe DSR shape grammar and a generative design frameworkthe User-inferred generative system with subjective design evaluation mechanism.In design process, designers always think the way how to transform a design before the final solution is confirmed. Inspired by the process, the dynamic information received form DSR shapes can be used to create novel alternatives conveniently. The DSR (Dynamic Shape Representation) shape represents a shape not only by the geometric and topological information (static), but also its generating process in terms of series of sequential design actions (dynamic). The new shape representation can provide flexible ways for more new shape generation in generative system.Based on the DSR shape, a 3D shape grammar and a general 3D interpreter are introduced for conceptual product design. The information process including design actions and steps of design creations can be represented by the proposed shape rules and design languages. Different from traditional shape grammars which are operated at the basis of shape replacement and sub-shape detection, I propose a new way to use shape rulesthe ACM model. It permits that using the same design language to different design cases (initial shapes) for novel exploration. Emergent shape is supported. Design languages are generated in 3D environment by designers and recorded by the proposed system. The rule-based mechanism can release designers from the limitations of pre-defined operating functions. The generative design system explores design alternatives in a huge solution space. It generates many inspiring design alternatives with more un-interested ones simultaneously. The user-interfered generative approach makes use of users' knowledge at the early stage by the design languages generated by DSR shape grammars. Through the interactions between design languages and designers, the preferences of design proceeding can be saved into the grammatical languages. After information digitalization, the parameters used in generative mechanism can represent users' intention. More useful design solutions will be created. For better interactive design evaluation, a subjective design aesthetic evaluation method is proposed for design exploration. There are several design examples shown in this thesis, such as the embroidery design, chair design and cup design.Information flow from design end to system end is valuable to guide the automatic mechanism towards to the positive direction effectively. The final solutions and actions in design process can be captured by the proposed 3D shape grammars, which can be used in the user-interfered generative framework. The whole process is not pre-defined by system.Designers can communicate with the interpreter by design languages in terms of design visualization.The newly designers' preferences included in design languages can be involved in the generative process at the later stage. The subjective evaluation model is useful to find the users' interesting solution space for deep design exploration. Therefore, the proposed framework can be suitable for the design innovation in conceptual design. |
| Author |
Leong, Kong Sang |
| Title |
Supporting the use of web-based crime mapping in cooperative policing by dynamic pattern analysis |
| Department | Dept. of Computing |
| Year | 2016 |
| Subject |
Digital mapping. Crime analysis -- Data processing. Hong Kong Polytechnic University -- Dissertations |
| Degree | Ph.D. |
| Pages | xviii, 300 pages : color illustrations |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2890630 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/8491 |
| Abstract |
This thesis reports on a map-centric spatial-temporal crime pattern analysis system -Dynamic Pattern Analysis system (abbreviated as DPA system). The term "dynamic pattern" does not refer to a particular type of spatial-temporal pattern. We use the term "dynamic" to reflect the dynamic and diverse nature of spatial-temporal crime patterns. The proposed DPA system consists of four modules: (1) Basic tendency analysis provides a general view of the distribution of crimes over space and time, (2) Spatial relation analysis identifies spatial relationships of crime patterns at different time points, (3) Cyclic Signature clustering makes use of similarities of calendric patterns to find hotspots with similar features, and (4) the Dynamic Relation model is a data-driven evaluation approach for analysing the interactions between spatial-temporal crime patterns and Web-Based Crime Map. Four types of dynamic relation (HI, HD, LI and LD), referring to different situations, can be identified by the Dynamic Relation model. The different types of dynamic relation can also be combined for analysing more complex spatial effects, such as displacement, aggregation, general increase and general decrease. These four modules are designed based on a comprehensive literature review and two international-wide studies. The modules unite to form an integrated system, yet each can be operated independently. Case studies are presented in order to evaluate this system based on the collected real-world data from the Hong Kong police force and London's crime map. All the results are in line with expert predictions and corroborated by related empirical crime studies. In addition, three additional case studies were conducted from May to August 2015 in order to further evaluate the information generated from the four different modules in the Dynamic Pattern Analysis system (DPA system). Different methods, such as survey and clustering performance evaluation were used for different evaluation purposes. According to the evaluation results of the three additional case studies, we found that making use of DPA output (i.e. information generated from the DPA approach) was better than making use of other benchmark output (i.e. information generated from the corresponding benchmark approach) in different aspects. In case study 1, we invited fifteen international crime analysis professionals, including three highly-cited scholars in spatial-temporal crime analysis, to participate in an online survey. We found that making use of DPA output enhanced the accuracy of analysis. Moreover, the results of the survey also indicated that making use of DPA output not only changed international professionals' police resource allocation decisions significantly, but also the decisions made were more suited to the local situation. In case study 2, we used a two-year theft-related dataset to create three transformed datasets in three different forms of temporal pattern. For each transformed dataset we conducted clustering. The clustering results were evaluated by using the measures (i) purity and (ii) genetic distance. We found that using DPA's form of temporal pattern (i.e. cyclic temporal pattern) for clustering can create clusters with higher intra-cluster similarities and lower inter-cluster similarities than using other forms of temporal pattern. In case study 3, we invited fourteen experienced crime analysis professionals to participate in an online survey. The results of the survey indicated that making use of DPA output not only changed their police resource allocation decisions significantly, but also the decisions made were in line with the corresponding crime prevention guideline. |
| Author |
Huang, Xinxin |
| Title |
Surface characteristics of low-twist worsted yarns and knitted fabrics |
| Department | Institute of Textiles and Clothing |
| Year | 2016 |
| Subject |
Woolen and worsted spinning. Yarn. Hong Kong Polytechnic University -- Dissertations |
| Degree | Ph.D. |
| Pages | xxxii, 259 pages : color illustrations |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2894554 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/8505 |
| Abstract |
Wool apparel and other textile products are of high value and popularity in the market all the time because of their aesthetic quality and comfort. With the increasing demand of light, thin and comfortable knitted fabrics, it is desirable to have wool yarns in medium to high counts with better yarn evenness, less hairiness, soft handle and reasonable tenacity, etc. By literature review, ring spinning continues to predominate in worsted yarn manufacturing industry because of its high quality of yarns and good flexibility in materials and yarn count. Many modifications have been conducted to enhance the control of fibers in spinning triangle and reduce yarn hairs, but nearly have no improvement on yarn soft handle and evenness. However,over ten years ago, a modified technology on the ring frame was developed by employing a false twisting device and a strand separator, which was named as Nu-torqueTM or low-torque or low-twist spinning. Since then, the technology has evolved in five versions. The low-twist cotton yarns exceed other types of modified ring spun yarns with respect to softer handle, lower residual torque, and outweigh the conventional ring yarns in aspects of higher tenacity, lower hairiness, etc. Previous versions of low-twist worsted yarn technology have produced low-twist worsted yarns in median and coarse count, however, some problems were found such as worse yarn optical evenness, more neps and tight wrapper fibers, as well as lower yarn tenacity, among which, the wrapper fibers give rise to obvious "bar effect" on the dyed knitted wool fabrics. Hence, this thesis is aimed at investigating these problems and exploring possible solutions from both theoretical and practical points of views. The surface structure of 24Nm low-twist worsted yarns are examined under Microscope Lecia M165 in details and classified into five types including three kinds of wrapping structures and two kinds of unwrapped structures. In particular, the tightly wrapping structures take up almost 60% on the low-twist yarns. These tightly wrapping structures not only bring about quite compact yarn structures resulting in harsh handle of yarns and fabrics,but also deteriorate yarn optical evenness resulted from obviously smaller diameters than conventional yarn structures and higher variations. Using high speed camera system, the formation of wrapper fibers on the low-twist yarn surface has been investigated. It is found that the abrasion between yarns or the protruding fiber ends and the upper false-twister or the lower false-twister, the fiber security of yarns in A zone, as well as the false-twisting effects exerted by the two false-twisters, have effects on the wrapper fiber formation; more importantly, the wrapper fibers have roots in the long protruding fiber ends in A zone on the low-twist spinning system, namely, the hairiness of 3mm and longer of the yarn segment between the spinning triangle and the false-twister. Besides, the bulked yarn segment resulted from excessive twists in A zone is reckoned as the reason for the formation of the curved yarns with tight wrapper fibers.Hypothesizing that the structure of yarn segment in A zone on the low-twist spinning system is similar to that of ring-spun yarns of a high twist without buckling, a hairiness model of such ring yarns is beneficial to understand the origin of hairiness and wrapper fibers as well as the formation of neps. The number of all fiber ends in the out-most layer of ring-spun yarn cross-section, which are already or have potentials to become hairs, is first defined as maximum hairiness in unit length of yarn. Based on Brown and Ly's work on the number of fiber ends in twist-less fiber assembly, a statistical model of the maximum hairiness of ring yarns has been established by considering yarn twist geometry and the contributing surface layer for hairs. In particular, fiber length, fiber cross-section and the number of fibers have been revised with the consideration of yarn twist. Moreover, Hairiness contribution factor (h0) is proposed for model development as the ratio of the number of fiber ends having potentials for hairiness and the total number of fiber ends in yarn cross-section. From the developed model, it can be seen that the maximum hairiness of ring yarns, or the number of long protruding fiber ends in A zone of the low-twist spinning system, relates to fiber length distribution, fiber diameter, yarn count, yarn twist,measured hair length etc. Moreover, the present model provides the length of the predicted maximum hairiness, whereas previous related models fail to do so. The verification by experiments demonstrates that the predicted values of 1mm and longer are in the same order of magnitude as the measured values, which are more accurate than the predicted values from other related models. Whereas, the predicted maximum hairiness of 3mm and longer, that is, the long protruding fiber ends, is almost 1~2 order of magnitude higher than the measured S3 values. Alternatively, there are some other ways to further reduce the number of long protruding fiber ends in A zone, like combining Siro-spinning or Solo-spinning with low-twist spinning, because it is generally believed that surface fiber trapping between the two substrands in Siro-spinning triangle or among several substrands in Solo-spinning triangle contributes to the significant decrease of yarn hairiness. Accordingly, the maximum hairiness model of ring yarns is revised for Siro-spun yarns and Solo-spun yarns with respect to fiber trapping and yarn geometry, respectively. Also, experiments have been carried out to verify the developed hairiness models. As aforementioned before, the fiber security of the yarn segment in A zone also influence the wrapper fiber formation and the resultant yarn surface; and the degree of fiber ends being tucked into yarn bodies directly determines the number of protruding hair of yarns. Whereas, the existing related parameters only describe fiber ends already protruding out of yarns. Similar to the theoretical limit of yarn evenness CVlim, the real yarn hairiness can approach but is always lower than the maximum hairiness of ring yarns. A Relative Hairiness Index (RHI) is accordingly proposed, which has two forms:the theoretical one and the actual one. The theoretical RHI is the ratio of maximum hairiness of certain type of yarn to the maximum hairiness of ring yarns, which can theoretically reveal the effectiveness of different spinning methods in tucking fiber ends into yarn bodies; and the so-called actual RHI is the ratio of the measured yarn hairiness and the maximum hairiness of ring yarns, which can actually demonstrate the degree of fiber ends potential for hairiness being tucked into yarns resulted from various spinning system or their spinning parameters. Both the theoretical RHI and the actual RHI demonstrate that Siro-spinning can most effectively tuck fiber ends into yarn bodies, therefore Siro-spun feeding will give rise to the least long protruding fiber ends. Additionally, winding is employed to mimic the abrasion that yarn will experience, and it is found that the hairiness of ring yarns obviously increases with the increasing winding times and reaches a plateau after the fourth winding, therefore the number of hairs of yarns after four-time winding, is termed as stable hairiness. By analyzing the increment rate of the actual RHI of various yarns in the states of cop, cone and stable, which are the yarns experience zero-time, one-time and four-time winding, respectively, Siro-pun yarns also present the best fiber security.Hence, Siro-spun feeding with a normal roving gap of 14mm is combined with the lately 5th version of low-twist spinning system for further reducing the wrapper fibers and improving the surface of low-twist yarns. However, aiming at yarn evenness and tenacity, as well as proper twists in A zone to avoid bulking as described before, the spinning parameters of 36Nm low-twist yarns (36LT) is first systematically optimized by means of the combination of Fractional Factorial Methodology and Response Surface Methodology, respectively. With a twist multiplier reduced by around 15%, the optimized 36LT yarns show comparable tenacity and similar hairiness, but still a bit worse evenness and more neps than the conventional yarns. Actually, the number of neps (+140%) has been reduced about one order of magnitude on the present low-twist yarns by comparing with that of yarns produced on the previous versions of low-twist spinning system. The blackboard evenness of the optimized 36LT yarns exhibits half grade lower than the conventional yarns with a twist multiplier higher by about 15%, but half grade higher than the counterparts with the same level of twist multiplier, respectively. Then, the spinning parameters of 36Nm low-twist yarns with double-roving feeding (36LT+Siro) are also optimized by using Response Surface Methodology. The tightly wrapped structures on the optimized 36LT yarns only account for 8.9%, whereas the ones on the optimized 36LT+Siro yarns even reduce to 5.8%.Moreover, nearly no tightly wrapped structures with a curved yarn body are found on the two optimized yarn surfaces. Therefore, the optimized spinning parameters of low-twist spinning system, as well as the incorporation of Siro-spinning not only facilitate the reduction of wrapper fibers on the resultant yarns, but also provide suitable twists in A zone to avoid producing buckling and curved yarn segments. Nevertheless, the optimized 36LT yarn has an obviously higher actual RHI than the conventional ring yarns, and it presents similar increment rate when enduring abrasion to that of its counterpart, which indicates that the optimized 36LT yarns possess low fiber tucking and security, in other words, the fiber deformation resulted from false-twisting effect fails to be held in yarns. But the actual RHI of the optimized 36LT+Siro yarn and its increment rate by abrasion are markedly lower than the ones of the conventional yarn, particularly, its increment rate is even similar to that of Solo-spun yarns. It is demonstrated that the fiber tucking and security of low-twist yarns can also be improved by integrating Siro-spinning system.Finally, using the Kawabata Evaluation System of Fabric (KES-F), the knitted fabrics made of the optimized 36LT yarns are examined in terms of fabric surface property, tensile and shear, as well as bending and compression. There are no statistically significant differences in surface property,tensile, shear, bending, compression and bursting strength between the low-twist fabrics and the conventional fabrics made of the worsted yarns with a higher twist multiplier by around 15% (at a significant level of 0.05). However, the low-twist fabric possesses better pilling performance and air permeability, but lower thermal conductivity than its counterpart. Besides, nearly no "bar effect" is found on the resultant fabrics made of the optimized 36LT yarns. |
| Author |
Liu, Xuqing |
| Title |
Surface functionalization of fibres with polymer brushes |
| Department | Institute of Textiles and Clothing |
| Year | 2015 |
| Subject |
Textile fabrics -- Surface properties. Textile fibers -- Surface properties. Polymers. Hong Kong Polytechnic University -- Dissertations |
| Degree | Ph.D. |
| Pages | ix, 192 pages : color illustrations |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2828509 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/8263 |
| Abstract |
Textiles with multiple functional properties are the future of the global textile and apparel industry offering new challenges as well as opportunities. A major application of these textiles will be in the field of functional clothing where the consumer is demanding more and more comfort, easy care, health and hygiene while at the same time expecting protection against mechanical, thermal, chemical and biological attacks. Along with the new functionalities,other desirable properties of finishes include the appearance,feel and durability to laundering. Such complex expectations can only be met by developing new, advanced and innovative technologies for finishing of textile products. To match the requirements of functional fabrics, in this thesis, a systematic study has been carried out to establish active interfaces by grafting polymer brushes on fabrics. These active interfaces are response to moisture, temperature, catalyst, and play as a platform to nanostructures deposition, and several functional fabrics are developed based on the active interface. The knowledge gaps identified in the introduction and literature review have been filled by carrying out the objectives which are summarized below. Firstly, to fill the research gap 1, activated single molecular layer which can both bond fibre with strong adhesion and process reactive chemical groups for further functional polymer brushes growth is developed. Trichlorosilane functionalized initiator for fabric substrates is designed and synthesized. It is proved that polymer brushes could be prepared by combining this designed initiator and the controlled living polymerization on the fabrics' surface,meanwhile commercial 2-bromoisobutyryl bromide is studied as a reference. The influence on two kinds of initiators for controlled growth of polymer brushes on cotton fabrics is investigated and the designed trichlorosilane functionalized initiator showed some advantage with the commercial 2-bromoisobutyryl bromide. To fill research gap 2, based on the activated single molecular layer on fibres, responsive polymer brushes are grown directly by the surface-initiated atom transfer radical polymerization (SI-ATRP), to construct a series of active interface on fibres. Poly(N-isopropylacrylamide) brushes which can built up thermal-responsive interface with water is selected since its low critical solution temperature (LCST, 31~35 °C) is similar to the body temperature. The grafted polymer brushes which can responsively and reversibly control the wettability and hygroscopicity of cotton, meanwhile the smart interface can switch from high water absorptive state below its LCST to low absorptive state above its LCST. Smart systems with properties of moisture management and thermoregulation are investigated systematically on human body. To fill research gap 3, a typical polyelectrolyte,poly-2-(methacryloyloxy) ethyl-trimethylammonium chloride (PMETAC) brushes are introduced onto the fibre, to form active polymeric interface which can catch catalyst moleculars from solution and fabricate nanoparticles-polymer brushes. The strong adhesion force between resultant metal composites and fibres leading to excellent mechanical and electrical stability under extensive rubbing, bending, stretching,and washing;and the conductivity can remain stable in air with proper choice of metal. To exploit applicability of this type of polyelectrolyte brushes bridged metal nanoparticles deposition on non-natural synthetic fabrics, plasma assistant grafting polymer brushes was developed.Then PMETAC brushes were grown from the active PET surface by surface initiated ATRP, which act as a platform for ELD of copper particles depositing to form polymer-bridges copper-PET hierarchical structures subsequently. This in-situ depositing approach ensures that the copper nanoparticles could distribute uniformly and continuously on the surface of PET fabric structure. As the site selection of polymer brushes, a new printing strategy that allows for the simple fabrication of high-performance flexible, foldable, and stretchable metal conductors on a wide variety of substrates at room temperature is developed. It is compatible with many printing methods by simply tuning the amount of delivering matrix polymer for specific ink requirement, so as to fabricate features with sizes ranging from sub-micrometer, to micrometer,centimeter, and even meter scales. Therefore, MACP is suitable for experimental prototyping (e.g.,using inkjet printing and DPN), as well as high-throughput fabrication (e.g.,screen printing). Therefore,it shows remarkable application potentials for plastic electronics, smart textiles, electronic skins,and biomedical implants and devices. To fill the research gap 4,composite of metal oxide nanoparticles and polymer brushes are integrated by active polymer brushes through interfacial connection. UV functional metal oxide materials, ZnO nanorods,have been electrolessly deposited on cotton fabrics successfully, meanwhile polyelectrolyte brushes play as supported catalyst capture interface.Surface morphological observation reveals that the process leads to the deposition of hexagonal prism crystallites, a characteristic morphology for the ZnO materials. The optical-UV spectroscopy studies indication those ZnO nanorods deposited on fabrics surface show active defense and shelter against UV radiation. The strong adhesion force between composite of ZnO-polymer brushes and fibres offers excellent wash fastness. To fill the research gap 5, fabrics with micro-nano-polymer brushes are developed. Antifouling polymer brushes are grafting on fabrics with multi-brushes structure. Settlement assays with microalgae/zoospores indicated that the multi-scale polymer brushes could successfully repel the settlement of microalgae/zoospores.In future,the testing in both static and dynamic sea water,especially in dynamic sea water will be carried on. Additionally, antibacterial properties of functional fabrics with nano-copper coating which are mentioned in Chapter 4 are also investigated as extension.It shows an important expanded application of copper nanoparticles-polymer brushes composite. By grafting polymer brushes on fibre,a novel system with active interfaces is constructed and shows responses under external stimuli,including temperature, moisture,chemical solution,and plays as platforms to interact with water, metal nanoparticles, pH values, giving smart, intelligent and interactive textiles. The novel strategy of constructing active interface can be employed to impart more functional properties on various fabrics in future. The active interfacial science of fibre established in this thesis bases on assimilation of different sciences and knowledges such as surface chemistry, organic synthesis, polymer science, nanotechnology, lithography, and biology. |
| Author |
Wong, Chi-chung Wilson |
| Title |
Surface modification of poly (ethylene terephthalate) (PET) by laser irradiation |
| Department | Institute of Textiles and Clothing |
| Year | 2002 |
| Subject |
Hong Kong Polytechnic University -- Dissertations Polyethylene terephthalate Materials -- Testing Irradiation |
| Degree | Ph.D. |
| Pages | xxii, 249 leaves : ill. ; 30 cm |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b1667768 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/3682 |
| Abstract | The thesis is aimed to study the surface morphological modification of poly (ethylene terephthalate) (PET) by pulsed UV laser irradiation. A study on the physical and chemical properties of the irradiated PET was reported. Laser irradiated surfaces were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC) and some other traditional physical methods. The resulting properties and the potential industrial application of the irradiated PET were studied. Polymers have been widely used across most industrial sectors due to their excellent physical and chemical properties. Besides, they are inexpensive and easy to process. However, when polymers are required for high value market or high performance products, the demand made upon these polymers can often not be satisfactorily fulfilled. The not always satisfactory performance of polymers has led to the consideration of introducing new finishing technologies. Besides, due to ever-increasing demands in designing new functional fibres for high value added products, new finishing / modification technology is essential. In recent years, there has been great interest for simple but efficient, dry and physical methods for surface modification of polymers. This is partly because of traditional wet chemical finishing processes involve the use of solvents, which are environmentally unfriendly. One of the most studied technologies is UV laser irradiation of polymer surfaces. It was known that polymer surfaces often developed a periodic roughness or ripple in the range of micron size by UV laser irradiation at fluence (laser energy, unit = mJ/cm2) above the ablation threshold i.e. high fluence irradiation. However, ripple could be reduced to sub-micron level by an irradiation energy below the ablation threshold with a polarized beam i.e. low fluence irradiation. The development of the high fluence ripple is believed to be due to an extremely high absorption coefficient of the polymer to the laser radiation, releasing the frozen-in tension fields, resulting in a self-organizing of material by convection. The low fluence ripple is believed to be induced by repeated periodic interference of the scattered and incoming waves created by a polarized beam. UV laser irradiation of polymers involves not only photothermal processes but also photochemical processes. In general, a chemical modification of the polymer by UV irradiation takes place in a limited thickness to the top several hundreds of nanometres or less and does not affect the bulk properties. It was observed the PET modified by high fluence would normally result in the deposition of debris on the treated surface. These debris are ionized and carbon rich materials which finally condense forming higher aggregates, resulting in a reduction of the O/C ratio. Conversely, modification of PET surface by low fluence irradiation led to oxidation and almost no ablation was detected. The increase of oxygen concentration on low fluence modified surfaces was probably due to a subsequent reaction with atmospheric O2 during irradiation. Polar oxidized groups like carboxyls were induced, together with the increased oxygen content, which has given a more hydrophilic character to low fluence irradiated surface. Modifications in textile properties due to laser irradiation were studied. Properties included fibre weight and diameter, tensile strength and elongation, yarn abrasion, bending, surface lustre, wetting, whiteness and air permeability. Some properties were observed to be advantageous to the material, while some would have adverse effects. Potential application of the laser treatment on polymer was conducted based on the study of the dyeing and adhesion properties. |
| Author |
Xie, Zhuang |
| Title |
Surface nanopatterning of functional polymers by parallel scanning probe lithography |
| Department | Institute of Textiles and Clothing |
| Year | 2015 |
| Subject |
Nanostructured materials -- Microscopy. Scanning probe microscopy. Hong Kong Polytechnic University -- Dissertations |
| Degree | Ph.D. |
| Pages | xx, 150 pages : color illustrations ; 30 cm |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2806866 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/7938 |
| Abstract | Engineering surface with patterned functional polymers is a crucial issue in a wide range of research fields. The recently developed parallel scanning probe arrays have emerged as promising candidates for desktop nanofabrication with high resolution and high throughput. Yet, there are only a few literature reports on the large-area patterning of functional polymer nanostructures via parallel SPL, with lack of fundamental understandings and practical applications. Moreover, it still remains some inherent limitations in current parallel SPL techniques regarding the resolution, uniformity and versatility. This thesis describes several approaches to tackle the challenges in the two aspects. The statement of challenges and objectives of this research is presented in the beginning, followed by a comprehensive literature review on nanopatterning techniques and a general introduction of methodologies. Next, Chapter 4 introduces the studies on ink transport in direct writing of polymers and applications of liquid polymer matrix. Chapter 5 states a molecular printing approach towards high-throughput fabrication of 3D polymer brushes. Chapter 6 describes the development of an apertureless polymer pen array to deliver both optical energy and materials. Chapter 7 addresses the uniformity challenge in polymer pen lithography through engineering the tip structure and new materials. Finally, Chapter 8 provides conclusions and future outlooks. First, direct printing of polymer ink materials was studied by dip-pen nanolithography (DPN) and polymer pen lithography (PPL). Two typical polymer inks were investigated, including polyelectrolytes and hygroscopic polymers. For polyelectrolytes, the ink transport was found to be tuned from molecular diffusion to liquid deposition mechanism by adding additives or using polymer pens. Moreover, a catalytic printing was developed for generating metal structures on flexible substrates by employing the hygroscopic polymer ink as delivery matrix and surface-grafted polymer as receiving matrix for catalysts. Second, by combining PPL with surface-initiated polymerization, for the first time we demonstrated the high-throughput generation of 2D and 3D complex polymer brush nanostructures over square-centimeter areas. The control on the 3D structures of polymer brush patterns was achieved by rational design of PPL parameters. Furthermore, the large-area patterned polymer brushes were explored as etching resists for micro/nanofabrication, as well as robust and versatile platforms for bioimmobilization. In addition to material printing, an apertureless polymer pen array was developed to enable serial writing with light at the sub-wavelength scale. This was achieved by combining the self-light-focusing polymer pyramids with an opaque coating on the flat backing regions. The elastomeric pens also show the capability of force-tuned illumination and simultaneous delivery of materials and optical energy. Furthermore, a novel dual-elastomer tip array was designed and fabricated to improve the resolution and the large-area uniformity in PPL. The ultrasharp tip with hard-apex, soft-base layered structure was verified to reduce tip deformation upon contact with the substrate by both experimental and mechanical simulation results, leading to decreased feature size and minimized size variation over large areas. In conclusions, large-area, high-throughput nanopatterning of functional polymers by parallel SPL is achieved through approaches of direct printing, surface-initiated growth and photochemical modification. Meanwhile, the development of apertureless cantilever-free pen array and dual-elastomer tip array will extend the patterning capability of SPL and lower the barrier for desktop nanofabrication. Given the broad applications of functional polymers and lithographic techniques, the work presented here is expected to have great impact on physical, chemical, material, biological and engineering fields. |
| Author |
Chan, Ka Yin |
| Title |
Surface pigments on cosmetic contact lenses and implications on safe contact lens wear |
| Department | School of Optometry |
| Year | 2015 |
| Subject |
Contact lenses. Contact lenses -- Care and hygiene. Hong Kong Polytechnic University -- Dissertations |
| Degree | Ph.D. |
| Pages | xx, 205 pages : illustrations |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2828153 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/8256 |
| Abstract |
Background: The use of cosmetic contact lenses (CCL) has become increasingly popular especially in Asian countries such as Korea, Taiwan,Singapore and China.The public can easily purchase CCL online, at cabinet stores, flea markets, department stores, and accessories stores. CCL not prescribed and dispensed from optometric practices are just commodities to the salespersons who have no proper training in contact lens care and handling.Lack of training poses a threat to wearers who are not provided with any eye examination, aftercare services, or advice on proper lens usage and care. The quality of these CCL is also an issue as there is a lack of information on the manufacturer, the pigments used, manufacturing process, and the colour printing process. With huge demand for CCL in the market and lack of regulations of the sale of CCL, there is a need to review the safety of CCL. To date, research on CCL is scarce. This is probably due to the relatively low popularity of CCL, particularly in Caucasian countries. It was not until recent years that CCL regained attention due to increasing popularity in Asian countries and reports of microbial keratitis cases related to CCL. There was therefore a need to investigate the characteristics of CCL, particularly surface pigment CCL, and their implications on safe CCL wear. Objectives: The objectives of this PhD study were to: 1. develop a method to determine the location and permanency of pigments on CCL 2.investigate the effect of surface pigments of CCL on microbial adherence 3. investigate cytotoxic effect of surface pigment of CCL on porcine corneal epithelial cells using the new porcine eye model(PEM) 4.investigate the effect of surface pigments of CCL on protein deposition Methods: Experiment 1: The permanency of pigments of five brands of CCL was tested using a cotton bud rub-off test.Each lens was removed from its blister pack and placed on the cleaned surface of an electronic scale to allow monitoring of the force applied when each lens was rubbed to ensure consistency of force applied (applied force between 110 230g) for all lenses.Any pigment coming off the lens surface was determined by examining the tip of the cotton bud for pigment transfer after every rub. The procedures were repeated on both front and back surface. Experiment 2: Fifteen brands of new CCL (five lenses of each brand) were challenged with Pseudomonas aeruginosa ATCC 9027. Three brands of lenses and their clear counterparts were also challenged with Staphylococcus aureus ATCC 6538 and Serratia marcescens ATCC 13880.Lenses were incubated in bacterial suspension immediately after they were removed from the blister packs or storage vials. After 24 hours,the lenses were removed aseptically and rinsed gently with phosphate buffered saline to remove loosely attached micro-organisms and the viable organisms adhered to the lenses were enumerated using an automated colony counter after plating. Experiment 3: In order to test the cytotoxic effects of CCL in an ex vivo model,improvements were needed to the existing porcine eye model. These modifications were required because the current model only allows two porcine eyes set up each time and there was no strict control of the surrounding temperature or humidity. A total of 57 porcine eyes were used and they were mounted on four test PEM with blinking and lacrimation simulation. The nictitating membrane of the porcine eyes was held by a movable arm connecting to a motor to simulate blinking. An infusion wing was set right above the cornea so that Dulbecco's phosphate buffered saline (DPBS) could be applied to the superior limbal region regularly to simulate lacrimation. Viability of the corneal epithelial cells was assessed with 0.4% trypan blue solutions three hours after the commencement of the experiment. Two controls were set up: control A was to assess cell viability immediately without any treatment and control B was to assess cell viability on PEM without blinking and lacrimation simulation after three hours.Back surface pigment CCL and the clear contact lens clear counterparts were pre-soaked in different multipurpose solutions (MPS) and hydrogen peroxide system for 24 hours. The CCL were then placed on the porcine eyes on PEM with blinking and lacrimation simulation. Cell viability was assessed after three hours of experiment using Annexin V-FITC/7-AAD kit. Experiment 4: Ten young adults aged 18-35 years old were recruited. Subjects were required to wear the contact lenses (two brands of CCL and one clear contact lenses of the same lens material) for eight to ten hours. At the end of a day's wear, the subjects returned to the clinic and the contact lenses were removed and collected for protein quantification. Results: Experiment 1: Only one brand of CCLs was found to have no pigment coming off after repeated rubs with a wetted cotton bud. The other CCL all had pigment transferred to the cotton bud after two rubs (Range: 1-7).Experiment 2:Surface pigment CCL showed significantly higher amounts of microbial colonization than their clear counterparts for all bacterial species tested (p<0.028). No significant differences in the amount of microbial adherence were observed between the sandwich design CCL lenses and their clear counterparts for all strains of micro-organisms (p>0.402).Experiment 3: No significant difference was found in the number of dead cells between the four test PEMs in both central (p=0.53) and peripheral cornea (p=0.19). There were significantly more dead cells (central and periphery) in the test PEMs compared to control A (p<0.01) but significantly less when compared to control B (p<0.01). The results showed that all MPS showed no significant difference in the percentages of healthy cells between the CCL and clear contact lenses (p>0.05). The number of early necrotic,late necrotic and apoptotic cells between CCL and clear contact lenses in all tested solutions were also not significantly different (p>0.05). Experiment 4: The results showed no significant differences in protein deposition between sandwich CCL (Median: 583 [Range: 362 - 980]) or surface pigment CCL (Median: 600 [Range: 483 - 892]) and clear contact lens (Median: 639 [Range: 347 - 731]). Conclusions:The rub-off test provided an indirect and simple method to determine the pigment location of CCL. Our study showed that CCL with pigments printed on the surface resulted in significantly higher bacterial adhesion.However,using the improved PEM showed that the cytotoxic effects of leachates from surface pigments CCL were not significantly different compared to those of clear contact lenses after three hours of exposure.Protein deposition on CCL, either sandwiched or surface pigments, after one day of lens wear, was also not different from those on clear contact lenses worn by the same subject. |
| Author |
Shen, Xuesong |
| Title |
Surveying-computing integrated approach to tracking a tunnel boring machine during microtunneling |
| Department | Dept. of Civil and Structural Engineering |
| Year | 2010 |
| Subject |
Hong Kong Polytechnic University -- Dissertations Tunneling -- Equipment and supplies |
| Degree | Ph.D. |
| Pages | xxi, 164 leaves : ill. (some col.) ; 30 cm. |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2393054 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/5933 |
| Abstract |
Effective resource management on dynamic jobsites is crucial to successful construction project delivery. Automation systems for positioning and tracking construction resources, such as equipment, materials, tools and laborers involved on the site, provide engineers with reliable operations data, enhanced situational awareness and more effective project control. Technological advances have opened up the prospect of applying state-of-the-art radio frequency (RF) technologies, such as the global positioning system (GPS) and the radio frequency identification (RFID), for resource tracking in construction engineering. The performances of RF systems, however, could be severely degraded and thus become unreliable, due to signal blockage, distortion or deterioration when applied in an enclosed or partially covered environment. This thesis research aims to tackle challenging resource tracking problems in the enclosed, complicated underground space of microtunneling construction. In such projects a steerable, remotely controlled tunnel boring machine (TBM) drills a subsurface utility tunnel with diameters generally ranging from 0.6 to 2.5 m. Accurate TBM tracking provides vital guidance to steering its advancement along an as-designed tunnel alignment in the underground space. However, on the majority of microtunneling sites, the TBM is only roughly guided by conventional laser alignment systems. The operators, therefore, still rely heavily on experiences for TBM steering and alignment control. Although advanced TBM guidance systems have been developed by integrating sophisticated mechanical, optical and electromagnetic subsystems, the high complexity of the system design can compromise system reliability, while considerably increasing the system's price and consumption cost. This research proposes an automated and cost-effective solution for precise TBM tracking through surveying-computing integration. A robotic total station is remotely controlled by preprogrammed procedures to automatically track and survey the observation points fixed on the TBM. Thus, the TBM's position in the underground space is mapped on the fly within millimeter level accuracy. Any deviations from the as-designed alignment can also be derived instantaneously. Furthermore, given the coordinates of a minimum of three observation points on the TBM, the TBM's orientation (as defined with its three body rotation angles of yaw, pitch and roll) is determined by applying sophisticated point-to-angle computing algorithms in real time, rather than by using any orientation gauges or instruments (such as inclinometers, gyroscopes and compasses). A Monte Carlo simulation approach is then formulated and applied in order to ensure the performances of the proposed solution satisfy practical application requirements in terms of the accuracy. Two well-established point-to-angle computing algorithms originating from space science and navigation engineering, the deterministic tri-axis attitude determination (TRIAD) algorithm and the optimal Quaternion method, are elaborated, evaluated and compared. Besides, four possible layout options for fixing a limited quantity of observation points on the TBM are considered in the simulations. A hardware-software integrated prototype of the proposed TBM tracking solution was developed in house for concept proving and verifying the application value. The prototype system has undergone extensive validation testing. Its functionality was first tested in the laboratory. With the assistance of industry partners, the practical applicability of the system was further verified over a three-month period in late 2009, on an ongoing microtunneling site in Hong Kong. Coupled with a 1.2 m diameter TBM, the system had been successfully implemented in tracking the installation of a 55 m long section of concrete tunnel. The TBM's position and orientation data were gathered automatically and completely. The data updating frequency was once per minute. The research has made essential contributions to the state of the art in resource tracking, computing and automation in construction engineering research. In terms of industrial contributions, the research has delivered a surveying-computing integrated, automated and cost-effective solution to tracking a working TBM in the underground space, holding high potential to advance the state of the practice in microtunneling operations. |
| Author |
Law, Ka-hung Rudy |
| Title |
A survey of Hong Kong software industry : in search of a competitive strategy for the small & medium size software firms |
| Department | Dept. of Management |
| Year | 2001 |
| Subject |
Computer software industry -- China -- Hong Kong Small business -- China -- Hong Kong Hong Kong Polytechnic University -- Dissertations |
| Degree | D.B.A. |
| Pages | ix, 174 leaves : ill. ; 30 cm |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b1604155 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/1295 |
| Abstract | This research tests the impact of product differentiation, product innovation, national innovation policy, and interfirm linkages on organizational performance. It is hypothesized that the first two constructs differentiation and innovation are positively related to performance. On the other hand, national innovation policy and interfirm linkages are considered as moderating the impact of the differentiation-performance and innovation-performance relationships. Competitive strategy research, particularly the generic strategy of Porter (1985) and Mintzberg's distinction of generic strategy (1988) underpin this research study. This model's framework was tested using a sample of Hong Kong software firms. Data collected from this cross-sectional survey sample (n=51) were subjected to factor and regression analyses and all of the six hypotheses tested. The strategy-performance results reinforce Mintzberg's claim that differentiation against their competitors does have a significant impact on a firm's performance. There is empirical support of a positive association between differentiation by image and support, and the software firm's return on equity. However, differentiation by price has a negative effect on return on equity. Contrary to expectations, differentiation by design and quality, along with undifferentiation do not show significant influences. The moderating impact of interfirm linkages on strategy-performance is partially supported by the factor of image differentiation which has a significant effect on the firm's return on equity, though with opposite hypothesized direction. The importance of a second moderator, national government policy, is also confirmed in terms of differentiation by quality and image. These variables show positive impacts through their moderating effects on the strategy-performance relationship. For the innovation-performance results, both the level of innovation and the firm size (i.e., control variable) demonstrate a direct effect on sales growth. Contrary to literature claims, it does not offer significant empirical support between internal skills and capabilities, firm characteristics, and extra-organizational factors on the firm's performance. The moderating effect of interfirm linkages and the national innovation policy also do not have a significant impact on the innovation-performance relationship. |
| Author |
Wang, Chao |
| Title |
Suspended-core photonic microcells made by post-processing micro-structured optical fibers |
| Department | Dept. of Electrical Engineering |
| Year | 2014 |
| Subject |
Optical fibers. Fiber optics. Photonics. Hong Kong Polytechnic University -- Dissertations |
| Degree | Ph.D. |
| Pages | xxi, 154 p. : ill. ; 30 cm. |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2681828 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/7385 |
| Abstract |
Micro-structured Optical Fibers (MOFs) have attracted plenty of research interests for their unusual properties such as endlessly single mode operation, high birefringence, high non-linearity, and novel dispersion. The MOFs with holey structure also provides degrees of freedom to modify their properties by post-processing techniques. In this dissertation, a novel technique has been demonstrated for fabricating in-line suspended-core (SC) photonic microcells by post-processing holey MOFs. The technique is highly flexible in making SC microcells with various cross-sectional shapes. These microcells may find versatile applications in photonic sensors and devices. The technique involves opening of selected air-hole at the end of a MOF, pressurization of the air-holes, and tapering the MOF at selected locations. The outcome is a photonic microcell with a SC section with reduced core dimension and significantly inflated air-holes. The microcells possess the unique properties of the SC fibers (SCFs), but avoid the problem of large connection loss with standard single mode fibers. The insertion loss resulted from the adiabatic transitions between the SC region and the MOF pigtails are typically less than ~0.2 dB at 1550 nm. This makes the microcells easier to be integrated into standard fiber optic systems. The air-holes surrounding the SC of a microcell can be made significantly larger and hence the outer cladding walls thinner than those of a typical SCF, making it easier to fill fluidic materials into the holes transversely through side holes, or fabricate micro/nano structures on the SC by, for example, using a focused femtosecond (fs) laser to scan across the fiber from side. Six types of SC microcells with different core-shape and core-number have been made by the novel post-processing technique. Numerical models based on the finite element method (FEM) have been developed to study the mode properties of three types of the microcells, namely the 6-, 4-, and 3-hole microcells made by inflating the innermost ring of holes of the PCF. As examples of applications, in-fiber accelerometers, refractive index (RI) sensors, optical gain cells, and long period gratings (LPGs) are made based on these cells. Based on a photonic microcell with a hexagon-like SC surrounded by six air-holes, a robust micro-cantilever accelerometer within the microcell was made by use of an fs laser micromachining system. The device demonstrated a linear response to acceleration with sensitivity ~2.5 mV/g and a flat frequency response up to 2.5 kHz. A photonic microcell with a rhombus-like SC and four surrounding holes exhibits a very high group birefringence of about 5 x10³. By filling RI oil into the holes and testing the microcell within a Sagnac loop, it is shown that the birefringence of the SC is highly sensitive to RI. With an oil-filled microcell, a temperature sensor with sensitivity ~3.04 nm/°C (corresponding to RI sensitivity ~9.1 x10³ nm/RIU) is demonstrated. Based on the RI change of gas under pressure, a pressure sensor with a sensitivity of ~0.31 nm/Bar (corresponding to RI sensitivity ~1.5 x10³ nm/RIU) is implemented. By use of a photonic microcell with a triangular-like SC and three surrounding holes, an optical gain cell was made by drilling holes from the side-walls of microcell and circulating the ethylene glycol solution of rhodamine 6G in the air-columns. A net optical gain of ~ 2.04 dB was experimentally demonstrated at 633 nm with a 1 cm-long microcell side-pumped by a continuous 100mW 532 nm green laser. LPGs in the SCs of 3-hole microcells were also made by use of an fs laser and a point-by-point inscription technique. |
| Author |
Leung, Suet-ha |
| Title |
Sustainable thermal comfort |
| Department | Dept. of Building Services Engineering |
| Year | 2008 |
| Subject |
Hong Kong Polytechnic University -- Dissertations. Heating. Air conditioning. Ventilation. Buildings -- Thermal properties. Buildings -- Environmental engineering. |
| Degree | Ph.D. |
| Pages | xx, 207, [70] leaves : ill. (some col.) ; 30 cm. |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2285797 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/3901 |
| Abstract | Ex-Premier Hon. Lee Guan Yew at the end of last Century, voted the invention of air-conditioning system as the greatest invention in 20th Century for Far East Asians because these systems keep indoor users comfortable in indoor spaces. The thermally comfortable environment helps to boost up the economy in Asia. ASHRAE Standard 55 on 2004 which is based on the late Professor Fanger's comprehensive thermal comfort theory provides the engineers a model to design and control the indoor thermal environment optimally. In geographically temperate regions, indoor cooling is the main issue for keeping an optimum thermal comfort environment. A survey conducted by Chan et al (1996) in the Hong Kong air-conditioned offices revealed that the thermal environment is not satisfactory. Two main reasons are identified in this project - distributive nature of the thermal environmental parameters and local culture. The former is not, and probably in many situations, cannot be properly controlled to match the thermal loading with the cooling capacity. The later influences the thermal comfort management protocol inducing unacceptability. In this thesis, two approaches are used to rectify the situation. Firstly, from further analysis of the large data base compiled by Chan et al., the most influential distributive natures are found to be the spatial and temporal distribution of the air temperature and the distribution of clo. It is further found that the Hong Kong people are almost 2 oC lower indulged as compared to ASHRAE Standard thermal comfort zone. The findings lead to a new sequence of design, test and commissioning and operation of the air-side systems in setting the optimum air temperature for control, fine tuning of the air distribution and control, and operation of the systems. An envelop of air temperature which is formed by the two extreme distribution functions at air temperature linked by the range of temperature swing is proposed as a new target of air temperature control function. In this integrated approach, education, space air lightness, air and water balances and company culture on clothing clo are all taken into account. Secondly, this study explores the feasibility of raising the air temperature in indoor space. Thermal comfort is maintained by increasing the velocity. Energy saving by replacing chilled water energy with fan energy is not the main target. In traditional thermal comfort management, cooled supply air is the main tool. In this study, loss of thermal comfort satisfaction due to the raised supply air temperature is compensated by higher air velocity and room air by-pass. A higher air velocity is produced by a special design of the fan coil system which is an integration of a traditional fan coil and an inverter control fan. The inherent deficiency of wall mounted thermostat can be reduced. Furthermore, a periodic fluctuation of air velocity is rendered possible which further enhances the thermal comfort. Hence, the new system is named "Harmonious Fan Coil System". The system is analyzed and found feasible by site testing and ample computational fluid dynamic computations. |
| Author |
Lee, Ka-lee Grace |
| Title |
Sustainable urban renewal model for a high density city : Hong Kong |
| Department | Dept. of Building and Real Estate |
| Year | 2009 |
| Subject |
Hong Kong Polytechnic University -- Dissertations. Sustainable urban development -- China -- Hong Kong. Urban renewal -- China -- Hong Kong. |
| Degree | Ph.D. |
| Pages | xxii, 359 leaves : ill. (some col.) ; 30 cm. |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2275552 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/3983 |
| Abstract | Like other developed countries in the world, the importance of urban renewal in improving the physical environment conditions and the living standards of the public is recognized in Hong Kong. However, many previous studies revealed that a lot of urban renewal projects failed to tackle the problems of urban decay and to satisfy affected parties, and brought the dilemmas and conflicts among the three domains: economy, environment and society. To address the deficiencies of current practices and ascertain the quality of the renewal projects, defining what constitutes a sustainable urban renewal project and how to implement it are crucial issues that have attracted considerable attention in academia and construction industry. In view of this, this study is initiated. The objectives of this research are to develop a sustainable approach in planning urban renewal projects to be conducted in Hong Kong by means of urban design; to identify the relationship between urban design considerations and the sustainable development objectives; to determine the underlying factors that contribute to sustainable urban regeneration and to derive a model for assessing the sustainability level of local urban renewal projects. Through comprehensive literature review, the urban renewal practices and their associated problems were clearly identified. Sustainability concept, value of urban design, design considerations enhancing triple sustainable development objectives, and their interrelationship were also explained. By adopting questionnaire surveys and various statistical analyses such as Independent T-test and Exploratory Factor Analysis, general views of the key stakeholders in Hong Kong on the significance of each design consideration for sustainable development, and the underlying factors that account for the variances in their perceptions could be found. Based on the factors highlighted, the assessment design criteria of the model were identified and its framework was also derived. This framework served as a hierarchy for conducting Analytic Hierarchy Process, which was used to find out the relative importance of individual design criteria and form the skeleton of the assessment model. In order to ensure that the model derived can effectively assess the sustainability level of local urban renewal projects, a valid assessment tool has to be made. Both qualitative and quantitative indicators were developed under various design aspects for benchmarking the project performance systemically. With the help of the experts from the industry and academia, the indicators have undergone a detailed evaluation process, which have revealed that the model composed of 34 indicators was a reliable and valuable tool to achieve the goal of producing sustainable urban renewal projects in Hong Kong. Critical factors meeting the sustainable development objectives and the assessment model are two major outputs of this study. The research findings help to strengthen the understanding of local developers, urban designers and government officials on how to plan a sustainable urban renewal project to create a sustainable community afterwards. They should take into account of those crucial factors extracted from an analysis of the sample opinions from relevant parties in order to attain excellent performance in local projects in the future. Furthermore, the assessment model suggested here can ascertain that local urban renewal projects carried out in the future can deal with the urban problems and benefit the community in various aspects effectively and efficiently because the impacts of the projects on economy, environment and society can be predicted in advance and necessary adjustment to the renewal proposals can also be made. Apart from its practical applications, this research is also useful in academia. Although there is abundant research studying the concept of sustainability and the value of urban design respectively, there are few attempts to combine them into urban redevelopment literature. There are a number of schemes and indicators available for assessing sustainable development, but they are not tailor-made for measuring the performance of urban renewal projects. Therefore, the findings of this research can enrich the contents of related topics. |
| Author |
Chan, Ping-tong |
| Title |
Symbiosis of fuzzy systems and genetic algorithms for modelling and control |
| Department | Dept. of Electrical Engineering |
| Year | 2000 |
| Subject |
Intelligent control systems. Fuzzy systems. Fuzzy logic. Genetic algorithms. Hong Kong Polytechnic University -- Dissertations. |
| Degree | Ph.D. |
| Pages | [15, 170, 31 leaves] : ill. ; 30 cm. |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b1498138 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/1418 |
| Abstract | In recent years, the integration of Fuzzy Systems (FS) and Genetic Algorithms (GA) has gained a lot of attention and many researchers have advocated exploiting the possibilities of this union. Essentially, FS is to provide GA a platform for the incorporation of linguistic IF-THEN rules and logic reasoning, and GA's role is providing FS with non-linear optimisation. The objectives of the studies undertaken in this thesis are to validate these arguments and to propose modelling and control algorithms for some classes of non-linear systems. The study will focus on problems such as optimisation speed, stability issues before and after optimisation, and high dimension systems. The findings are verified through benchmark simulation and experimental trials. The studies are carried out in three phases. In the first phase, a method to model a plant's data is proposed. An Antecedent Validity Adaptation (AVA) principle is introduced to refine Table Look-up (TL) scheme. The term Table Look-up with Validity (TLV) is coined as a scheme for modelling recorded data. The proposed technique is endowed with the ability of using the dormant and hidden information in the available data. An on-line algorithm is also presented. The design of an Optimised Fuzzy Logic Controller (OFLC) is introduced next. With the aid of genetic algorithms, optimised rules of fuzzy logic controller are designed. The use of symmetric properties to save the number of learning rules is described. The proposed algorithm has been applied to both linear and non-linear systems. This algorithm cuts the vast tangle of the rule-table down to size by incorporating the physical properties of systems and mechanisms of GA. Then OFLC is employed to control a beam-and-ball balance hardware test-bed. A Kalman filer controller (KFC) and a manually tuned fuzzy logic controller (MFLC) are also developed to assess the effectiveness of the OFLC. The proposed controller provides favourite performance in a systematic design manner. In the second phase, a supervisory control technique is applied to an integrated Sliding Mode Control (SMC)/FS. An Indirect Adaptive Fuzzy Sliding Mode Control (IAFSMC) with supervisory controller is proposed which guarantees the boundedness of states of the controlled system and parameter projection to avoid the divergence of the parameters. Along this line, an integrated stable FS+GA system is proposed, in which the FS is optimised by GA. A state supervisory controller, studied in the IAFSMC, is used to guarantee the stability. In the third phase, the use of Hierarchical and Fused FS (HFFS) will be discussed to alleviate the explosion of dimension. The design of an Optimised Hierarchical and Fused Fuzzy System (OHFFS) will be introduced which uses the divide-and-conquer technique to separate a large GA/FS optimisation problem into a series of more manageable problems. The fused FS is applied to the cart pole system and the hierarchical FS is employed to the truck-and-trailer system. |
| Author |
Xiong, Tao |
| Title |
Symbol-level information extraction : from bits to symbols in wireless network cross-layer design |
| Department | Dept. of Computing |
| Year | 2015 |
| Subject |
Wireless communication systems. Cross-layer designs (Telecommunications) Hong Kong Polytechnic University -- Dissertations |
| Degree | Ph.D. |
| Pages | xviii , 143 pages : color illustrations |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2813362 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/8021 |
| Abstract |
At ever-increasing rates, wireless networks are becoming an indispensable part of people's daily life due to the low cost in the deployment of networking infrastructures and the high availability to access the Internet. Current wireless technologies use bits to deliver both the digital contents and packets' information, e.g. MAC address or packet transmission duration, which require the packets to be fully received and correctly decoded. However, for most receivers in the networks, they only need packets' information to adjust their behaviors even if they suffer the bad channel conditions. In this thesis, I mainly focus on the cross-layer design of symbol-level information extraction which enables the vital information to be delivered between the transmitters and receivers at symbol-level. I further take advantage of that symbol-level information to design the cross-layer structure to deal with three popular research topics in wireless communications: the hidden terminal problem, the energy inefficiency of the packet overhearing problem and communications security (COMSEC) problem. Hidden terminals are typical interference sources that can significantly reduce the throughput of a wireless network if it adopts the CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) MAC protocol. Normally, the standard RTS/CTS (Request to Send/Clear to Send) mechanism is deployed to solve this hidden terminal problem. However, the standard RTS/CTS would fail to silence all the hidden terminal, as in the real world, the CTS packets might not be correctly received all the time due to either the CTS packets are unable to be decoded at remote hidden terminals or the CTS packets are collided with other packets at the hidden terminals. To solve the two drawbacks of the CTS packets, the RTS/S-CTS mechanism is proposed, which uses the symbol-level information extraction mechanism to deliver the NAV time information. The S-CTS frame can be correctly detected from collisions and by remote hidden terminals. Thus, the NAV time information which is contained in the S-CTS frame can be used to silence those hidden terminals. A testbed of RTS/S-CTS with GNURadio/USRP2 software radio is built to demonstrate its feasibility and extensive ns-2 simulations are conducted to evaluate its performance. The simulations results show that the RTS/S-CTS can significantly improve the throughput in the random topology network scenario compared with the standard RTS/CTS. In the energy inefficiency of the packet overhearing problem, I first reveal that the energy waste on the packet overhearing accounts for the majority of the energy inefficiency of wireless devices in high traffic wireless LANs by analyzing the real world traffic traces. Though there are many existing approaches trying to reduce this energy inefficiency, none of them can avoid the energy waste on the packet overhearing in high traffic wireless LANs effectively. Thus, I propose a novel SASD (Sample-Address Sample-Duration) scheme that uses the symbol-level information extraction mechanism to deliver the MAC address and packet transmission duration information at the PHY layer. The SASD enables the wireless devices to discern the information under the energy-saving downclocking mode through the SASD Detection and Identification decoder. Consequently, the devices which are not the intended receiver of the packet can switch to the sleeping mode to save the energy cost on the packet overhearing. The extensive hardware experiments and simulation results show that the SASD can greatly outperform the existing approaches in the high traffic wireless LAN scenario. In the wireless communications security problem, I explore the feasibility of symbol obfuscation to defend against the passive eavesdropping attack and fake packet injection attack during the wireless communications. I propose a novel Multiple Inter-symbol Obfuscation (MIO) scheme, which utilizes a set of artificial noisy symbols, which called "symbols key", to obfuscate the original data symbols in the PHY layer. As the symbols key information can only be extracted and verified by the legitimate receiver, the eaves-dropper can hardly decrypt the obfuscated symbols from the eavesdropped packets, and the fake packet can be easily checked out. Thus, the MIO can effectively enhance the wireless communications security. Compared with other communications security methods, the mathematical analysis proves that the MIO can provide the better performance on computational secrecy against the fake packet injection attack. Moreover, MIO can provide an easier way to achieve information-theoretic secrecy against the passive eaves-dropping attack. To sum up, by investigating the symbol-level information extraction mechanism to solve the problems, we show the feasibility of delivering vital information at the symbol level. Moreover, this symbol-level information extraction mechanism opens up a new dimension to convey the information from the bit level to the symbol level. |
| Author |
Zhao, Qingqing |
| Title |
Synaesthesia, metaphor, and cognition : a corpus-based study on synaesthetic adjectives in Mandarin Chinese |
| Department | Dept. of Chinese and Bilingual Studies |
| Year | 2018 |
| Subject |
Hong Kong Polytechnic University -- Dissertations Chinese language -- Semantics Mandarin dialects |
| Degree |
Ph.D. |
| Pages | xiii, 212 pages |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/99102214 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/9509 |
| Abstract | Linguistic synaesthesia involving description of one sensory modality in terms of concepts from another sensory modality, such as sweet voice and 冷色 leng3 se4 'cold color', is employed across discourse types (i.e., poetic and ordinary), time periods (i.e., synchronic and diachronic), and language families (e.g., Indo-European, Sino-Tibetan, and Semitic). The kind of language use has, however, not received much attention in linguistic research, although manifesting as mapping from one bodily domain to another bodily domain would pose challenges to Conceptual Metaphor Theory and the theory of embodiment. This thesis thus aimed to conduct a systematic and comprehensive lexical semantic study on linguistic synaesthesia of Mandarin sensory adjectives from a corpus-based approach, to explore the tendencies of Mandarin synaesthesia, and to examine the theoretical implications of linguistic synaesthesia. This study proposed a linguistic synaesthesia identification procedure (LSIP) to extract synaesthetic data for Mandarin sensory adjectives from the Sinica corpus, which was adapted from Pragglejaz Group (2007)'s well-established metaphor identification procedure (MIP). The proposed identification procedure for linguistic synaesthesia was demonstrated to be also applicable to other languages from other corpora. Based on the distribution of the collected synaesthetic usages of Mandarin sensory adjectives, the study found that Mandarin synaesthesia exhibited directionality mapping from more embodied senses to less embodied ones, analogous to the attested patterns of linguistic synaesthesia in Indo-European, Hebrew, and Indonesian languages. The directionality of Mandarin synaesthesia is, however, tendencies-based. In addition, Mandarin synaesthesia was attested to show language-specific characteristics when compared to the established tendencies of English synaesthesia, hence inconsistent with the proposal of cross-lingual universality of synaesthetic patterns. The distribution and directionality of Mandarin synaesthesia demonstrated that neither the embodiment account nor the biological association account of linguistic synaesthesia could be fully supported. The thesis thus suggested an incorporated theoretical model containing both embodiment mechanisms and biological mechanisms, to account for the synaesthetic tendencies of Mandarin sensory adjectives and the language-specific characteristics of linguistic synaesthesia in Mandarin Chinese. Besides, this study has shown that linguistic synaesthesia is a type of metaphor as a linguistic realization of conceptual metaphors, which should be taken into consideration by Conceptual Metaphor Theory. The thesis therefore argued for a finer-grained account of embodiment covering the notions of the degree of embodiment and the type of embodied events, to refine Conceptual Metaphor Theory and the theory of embodiment. |
| Author |
Wu, Ting |
| Title |
Synchrophasor technology and its application in power system |
| Department | Dept. of Electrical Engineering |
| Year | 2017 |
| Subject |
Electric power systems -- Mathematical models. Electric power systems -- Reliability. Electric power system stability. Hong Kong Polytechnic University -- Dissertations |
| Degree | Ph.D. |
| Pages | xv, 158 pages : color illustrations |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2952797 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/8884 |
| Abstract |
The recent system blackouts triggered tremendous interest for wide-area situational awareness (WASA) which is based on synchrophasor measurements obtained from Phasor Measurement Units (PMUs) or PMU-enabled Intelligent Electronic Devices (IEDs). Synchrophasor technology has become an essential component in the power system for enhancing grid reliability, detecting islanded sections, aiding in system restoration, and enabling state estimator algorithms to converge with higher accuracy. These applications require accurate synchrophasor measurements from multiple synchronized devices to provide a valid picture of the dynamic behavior of the system. However, the existing commercial PMUs have poor response under dynamic conditions, such as frequency deviation, amplitude/phase angle abrupt change and modulation. This thesis is devoted to developing an advanced synchrophasor measurement algorithm which can provide accurate phasor estimation under both steady and dynamic conditions, and apply the synchrophasor technology in power systems for fault location and state estimation (SE) in order to promote the existing WASA beyond its standard purposes of monitoring, observation and post-mortem analyses. First, an intelligent phasor estimation algorithm based on random forest (RF) technology is proposed to improve estimation accuracy with reduced latency. This algorithm pre-analyses the input signals to identify step change using Lipschitz Exponent (LE) and Wavelet Transform (WT), then the negative impact (deteriorating the accuracy of phasor estimation) of which is eliminated using an adaptive data window. Next, parametric signals are categorized into three types, i.e., signals containing harmonics, inter-harmonics, and others, by a well-trained RF classification model. For the first two categories, RF regression models are developed to eliminate both harmonics and inter-harmonics in phasor measurement. Besides, Clark transform with variable phase compensation (VPC) method is proposed to precisely track the true phasor for the third type of signals. Secondly, a fault-location technique, aimed at accelerating restoration, reducing crew repair costs, and enhancing the reliability of delivery in power systems, is developed for multi-terminal multi-section non-homogeneous transmission lines which combine overhead lines with underground power cables, by using voltage and current synchrophasors obtained from PMUs. Specifically, a faulty branch selector is first proposed to narrow down the suspected faulty area. Then, the faulty section and the exact fault location can be identified by calculating the normalized fault distance for each section on the selected faulty branch. The computational burden of the proposed analytical scheme is very low because it avoids iterative computations. Lastly, a fast state estimator and corresponding bad data (BD) processing architecture are presented to incorporate a limited number of PMUs into power system SE which plays a key role in the effective operation of power markets and enables real-time security assessment of power systems. The conventional measurements are processed by a three-stage SE method composed of two weight least squares (WLS) linear problems and a nonlinear explicit transformation in between. Then, the power system is decomposed into PMU observable and unobservable areas. The PMU observable states are calculated by a linear estimator, whereas the pseudo state values with large variances are assigned to PMU unobservable states. The results obtained from the above two estimators are then combined using the estimation fusion theory. Bad phasor measurements and bad conventional measurements in the PMU-observable area are identified and processed all at once, which can dramatically reduce the implementation time. |
| Author |
Chen, Yixin |
| Title |
Syntheses and applications of novel chiral ligands |
| Department | Dept. of Applied Biology and Chemical Technology |
| Year | 2000 |
| Subject |
Asymmetric synthesis Catalysis Chirality Hong Kong Polytechnic University -- Dissertations |
| Degree | Ph.D. |
| Pages | xiv, 168 leaves : ill. ; 30 cm |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b1524910 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/1972 |
| Abstract | Homogeneous asymmetric catalysis is currently one of the most actively pursued research areas in chemistry. Asymmetric catalytic reactions promoted by chiral transition metal complexes have been significantly advanced in the past two decades. A great number of optically pure compounds have been synthesized and used as chiral ligands. From both academic and practical standpoints, it is highly desirable to design and synthesize new chiral ligands and to test their applications in the asymmetric syntheses of high-valued pharmaceuticals and chiral intermediates. The novel chiral phosphinite l,2,5,6-di-isopropylidene-3,4-bis(diphenylpho sphino)-D-mannitol (DIMOP) was designed and synthesized by reacting chlorodiphenylphosphine with a D-mannitol derivative. This ligand has been found to be highly effective in the Rh-catalyzed enantioselective hydrogenation of amidoacrylic acid and its derivatives. Excellent enantioselectivities ranging from 90% to 97% were obtained. A new C2-symmetric heterocyclic chiral ligand, 6,6'-dihydroxy-5,5'-biquinoline (BIQOL) was also synthesized and tested in asymmetric catalysis. BIQOL ligand was easily synthesized via the oxidative coupling of 6-hydroxyquinoline in the presence of a CuCl2-benzylamine complex. Resolution of the BIQOL racemate was carried out via the chromatographic separation of its triflate derivative on a chiral OD column and subsequent hydrolysis. As expected, Ti-BIQOL catalyst was highly effective for the enantioselective addition of diethylzinc to a variety of aldehydes. It has been found that the diethylzinc addition to aldehydes catalyzed by Ti-BIQOL complex provided chiral products with good enantioselectivities (81-91% ee). The trialkylaluminium addition to aldehydes catalyzed by Ti-BIQOL complex was also studied and good results were obtained. Besides the success in the synthesis of phosphinite ligand DIMOP and heterocyclic ligand BIQOL and their application in asymmetric catalysis, a chiral diamine, 6,6'-dimethoxy-2,2'-diaminobiphenyl was also prepared from m-nitrophenol via iodine mediated Ullmann coupling, reduction and resolution. Novel chiral aminophosphine ligand 6,6'-dimethoxy-2,2'-bis(diphenylphosphinoamino)-l,l'-biphenyl (DMBDPPABP) was synthesized through the reaction of the corresponding diamine with BuLi and chlorodiphenylphosphine. Good enantioselectivities were found for the asymmetric hydrogenation of dehydroamino acid and its derivatives catalyzed by the cationic Rh-DMBDPPABP complex. The asymmetric hydrogenation of amidoacrylic acid and its derivatives were carried out under mild conditions, the products were obtained in 73-81% ee. (Lower enantioselectivities were observed in the hydrogenation of enamides catalyzed by Rh-DMBDPPABP.) Another novel chiral diamine derivative Ts-DMBDPPA was synthesized. Application of the ligand in the Ru-catalyzed asymmetric transfer hydrogenation of aromatic ketones was studied, and chiral alcohols were obtained with moderate enantioselectivities (62-78 % ee). |
| Author |
Lam, Fuk-loi |
| Title |
Syntheses of ferrocene-motif N-P/S mixed-donor ligands and their applications in construction of chiral carbon-carbon and carbon-heteroatom bonding via asymmetric allylic substitutions |
| Department | Dept. of Applied Biology and Chemical Technology |
| Year | 2008 |
| Subject |
Hong Kong Polytechnic University -- Dissertations. Asymmetric synthesis. Catalysis. Chirality. |
| Degree | Ph.D. |
| Pages | xvii, 255 leaves : ill. ; 30 cm. |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2239225 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/103 |
| Abstract | P/S chelating mixed-donor ligands have attracted recent attention in synthetic applications and showed excellent results in several asymmetric catalyses, such as transition-metal-catalyzed asymmetric allylic substitutions (AAS), asymmetric hydrogenation and aza-Diels-Alder reaction etc. In this thesis, we have designed and synthesized a family of newly developed fine-tunable phosphinamidite-thioether ligands with a ferrocene motif, which are easily accessible from the readily available Ugi amine as a chiral building block. The class of ferrocenyl phosphinamidite-thioether ligands is named as (S,pR)-FerroNPS which reflects its characteristic scaffold, chelating moiety, chirality on central and planar asymmetry. The transition-metal-catalyzed asymmetric allylic substitutions (AAS) have become one of the most powerful tools for the enantioselective formation of carbon-carbon and carbon-heteroatom bonds due to its versatile variation of nucleophiles. The family of (S,pR)-FerroNPS ligands have been successfully applied in the palladium-catalyzed asymmetric allylic alkylation (AAA) as the prototypical reaction to evaluate their usefulness leading to excellent isolated yield and enantiomeric excess in up to 99%. In a similar vein, the use of a mono-fluorinated nucleophile, a potential biologically active functionality, gave the corresponding optically active product in up to 93% ee. In addition to carbon-carbon bond formation, various amines were examined to afford the desired products containing a carbon-nitrogen bond in excellent yields and enantioselectivities (up to 96%). There are very limited cases in which the enantioselective version of palladium-catalyzed C-O bond formation has been accomplished by an allyic substitution protocol. It has been demonstrated that our Pd-(S,pR)-FerroNPS catalysts are generally effective and versatile to achieve C-O bond forming reaction with up to 96% ee. Significantly, hitherto unreported electronic effect of non-conjugated substituents on benzylic alcohols on enantioselectivity was observed. |
| Author |
Lam, Kin-ming |
| Title |
Synthesis and characterization of gold nanoparticles capped with tiopronin-derivatives and pyrrolidinium ionic liquids |
| Department | Dept. of Applied Biology and Chemical Technology |
| Year | 2011 |
| Subject |
Nanoparticles Ionic solutions Hong Kong Polytechnic University -- Dissertations |
| Degree | Ph.D. |
| Pages | xi, 312 leaves : ill. ; 30 cm. |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b2441572 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/6113 |
| Abstract | Nanoparticles have widespread applications in many areas and are a new generation of advanced materials. Among the different kinds of nanoparticles, gold nanoparticle is one of the most widely studied and utilized. The easy preparation, higher stability, low toxicity and unique properties make the gold nanoclusters the material of choice in many applications. The objective of this study is to synthesize and characterize a series of gold nanoparticles capped by different ligands. In the first part of the thesis, the preparation and characterization of several tiopronin derivatives and their gold nanoparticles were demonstrated. The tiopronin derivatives were designed by modifying their hydrophobic segment or the amino acid residue based on the parent tiopronin. The phenyl, ethyl, alanine, proline and leucine derivatives were synthesized. All, except the phenyl-, tiopronin derivatives gave stable, water-soluble and very small gold nanoparticles. The gold nanoparticles were characterized by IR, UV-visible, transmission electron microscopy, luminescence spectroscopy and thermogravimetric analysis. In the second part of the thesis, the ligand exchange reaction involving the tiopronin derivatives on the small gold nanoclusters was studied. The difference in structure of the derivatives did not introduce much discrimination on the extent and kinetics of the ligand exchange reactions. However, introduction of negative charges on the ligand monolayer on gold nanoparticles by pH adjustment significantly reduced the extent of exchange reaction at the initial stage and allowed the investigation of ligand exchange occurring at the higher energy metal surface defective sites. A difference in the exchange kinetics among different tiopronin derivatives was observed at pH 6.5. The initial stage for all exchange processes with tiopronin derivatives can generally be described by the second order Langmuir diffusion-limited model. This confirms the diffusion nature of the ligand exchange reaction between tiopronin and its derivatives on gold surface before equilibrium was established. In the third part of the thesis, the preparation of gold nanoparticles by direct reduction with tetrabutylammonium borohydride in neat pyrrolidinium-based bis(trifluoromethanesulfonyl)imide ionic liquids was studied. The average size of the gold nanoparticles prepared was 4 - 8 nm in diameter. The size-dispersity and colloid stability were improved when the nanoclusters were synthesized in longer alkyl chain pyrrolidinium ionic liquids. The presence of bromide only produced spherical nanoparticles while chloride could induce the formation of thread-like structure. A lower reaction temperature generally leads to a wider spread of average particle size of the gold nanoparticles. |
| Author |
Man, Man-lok |
| Title |
Synthesis and characterization of heterobimetallic complexes and their application on conversion of carbon dioxide to organic compounds |
| Department | Dept. of Applied Biology and Chemical Technology |
| Year | 2003 |
| Subject |
Hong Kong Polytechnic University -- Dissertations. Organic compounds -- Synthesis Carbon dioxide Laminated metals Electronic dissertations E-thesis |
| Degree | Ph.D. |
| Pages | xxvi, 223 leaves : ill. ; 30 cm |
| Language | English |
| OneSearch | https://www.lib.polyu.edu.hk/bib/b1732868 |
| URI: | http://theses.lib.polyu.edu.hk/handle/200/707 |
| Abstract | The heterobimetallic complexes [(n5-C5R5)Ru (CO)(u-dppm)M (CO)2(n5-C5H5)](M = Mo,W.; R=H , CH3)(1-4) are prepared by metathetical reactions between (n5-C5R5)Ru(dppm)Cl and Na+[(n5-C5H5)M(CO)3]-.IR spectroscopic and X-ray structural studies show that each of these complexes contains a semi-bridging carbonyl ligand. The low activity of these complexes in catalytic CO2 hydrogenation to formic acid can be attributed to the non-facile rapture of the metal-metal bond to yield the active metal dihydride species.The metal-metal bonds can be protonated to form the cationic complexes , which contain strong Ru-H-M bridges but no metal-metal bonding interaction . The bridging hydrogen atom is weakly acidic since it can be removed by a strong base, and it protonates BPh4- to give BPh3 and benzene. The protonated species also reacts with the hydridic hydrogen of Et3SiH to yield H2; the hydridicity of the hydrogen of Et3SiH is enbanced by attachment of a chloride anion to Si to form the adduct Cl-...SiEt3-H. The bridging hydrogen, however, cannot be removed by hydride scavengers such as Ph3C+OTf and Me3Si+OTf. The sluggishness of the catalytic formic acid decomposition by l-4 is attributable to the stability of the protonated bimetallic intermediate [(n5-C5R5)Ru (CO)(u-dppm)(u- H)M (CO)2(n5-C5H5)]+ HCOO- formed during the catalysis. The second part of the research concerns the synthesis of the heterobimetallic complexes [(n5-C5R5)Ru (CO)(u-dppm)Mn(CO)4] (7) and {[n5-C5(CH3)5]Ru(u- CO)2(u-dppm)Mn(CO)3} (8) and studies of their reactivities. These complexes were prepared via a novel synthetic method by reacting (n5-C5R5)Ru(dppm)H (R = H,CH3), a relatively hydridic metal hydride species , with HMn(CO)5 , a relatively protonic metal hydride species. X-ray structure study shows the existence of a semibridging carbonyl ligand in 7. Complex 8 consists of two bridging carbonyl ligands, along with the metal-metal bond. Both 7 and 8 can also be prepared by metathetical reaction between (n5-C5R5)Ru (dppm)Cl with LiMn(CO)5. Our work served as an example of the synthetic method concerning the use of two different meta1hydride species. Relaxation time T1(min) measurement and NOE study show that there is only weak dihvdrogen-bonding interaction between the two metal hydride species (n5-C5R5)Ru (dppm)H and HMn(CO)5 at room temperature. However, H/D exchange between (n5-C5R5)Ru (dppm)D and HMn(CO)5 was observed, implicating the existence of dihydrogen-bonding interaction between the species (n5-C5R5)Ru (dppm)H and HMn(CO)5, and the intermediacy of an n2-dihydrogen species. The catalytic activity in CO2 / epoxide coupling reactions of 7 and 8 were studied. It was found that both 7 and 8 catalyzed the coupling reaction of CO2 with a series of oxiranes to afford the corresponding cyclic carbonates in good yields. It was 1earned that both the steric and electronic properties of the oxiranes influenced the rate of the reaction. Two possible pathways for the 7-catalyzed CO2 / oxirane coupling reaction were proposed. The reactivities of the monometallic fragments of 7 and 8 had also been studied and compared with that of 7 and 8. Only the species Li+Mn(CO)4(PPh3)-(9)showed catalytic activity towards the coupling reaction, which is lower than that of 7 and 8. It is believed that the proximity of the metal centers in 7 and 8 is one of the reasons for their showing high catalytic activity; the two metal centers of the complexes act synergistically in the catalytic reaction: the manganese center reacts with CO2 to generate the metallocarboxylate anion, and the oxirane is activated by coordination to the ruthenium center via the oxygen donor atom. The species [(n5-C5H4)PPh2] Ru(PPh3)2H (10) which contains a Cp-tethered phosphino group was pepared by refluxing (n5-C5H5)Ru(PPh3)2Cl and KPPh2 in THF. A symmetric bimetallic complex {[(u-n5-C5H4) PPh2]Ru(PPh3)Cl}2 (11) was obtained by refluxing a CDCl3 solution of 10. The X-ray structure of 11 showed that there is no Ru-Ru bond,and the (C5H4PPh2) ligands are arranged in transoid configuration. The reaction of TpRu(PPh3)(CH3CN)Cl with 1.1 equiv of pyrazole resulted in the production of TpRu (PPh3)(pzH)Cl (12) On the other hand, a dimeric species [TpRu(PPh3)(u-pz)]2 (13) was formed when TpRu(PPh3)(CH3CN)H was reacted with 1.1 equiv of pyrazole. This synthesis is believed to be promoted by hydrogen-bonding interaction between the N-H of the coordinated pyrazole and the ruthenium hydride species. |