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Author	To, Pui Hang
Title	Temperature projection in Hong Kong using remote sensing and dynamic modelling
Department	Dept. of Land Surveying and Geo-Informatics
Year	2012

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Subject	Temperature measurements. Temperature measurements -- Remote sensing. Hong Kong Polytechnic University -- Dissertations
Degree	M.Phil.
Pages	x, 94 p. : ill., col. maps ; 30 cm.
Language	English
OneSearch	https://www.lib.polyu.edu.hk/bib/b2530162
URI:	http://theses.lib.polyu.edu.hk/handle/200/6757
Abstract	Temperature projections for Hong Kong have been carried out by the Hong Kong Observatory (HKO) in recent years. These projections have largely been based on the local climate data collected at the HKO Headquarters, and data obtained from the Intergovernmental Panel on Climate Change (IPCC). These projections have only been able to reflect the expected temperature change at the HKO Headquarters site, but have paid little attention to the effects of global warming and urbanisation at local scale across the whole of Hong Kong. This research has examined temperature changes due to both global warming and urbanisation effects independently and applied them over the whole of Hong Kong. The effect of global warming on temperature was estimated by regressing the IPCC data against the background temperature recorded at the Ta Kwu Ling (TKL) climate station, which is assumed to be free from urbanisation. Results showed that background temperature in Hong Kong will rise between 0.10℃ and 1.29℃ (with an ensemble of 0.67℃) in total in the next three decades depending on the amount of carbon dioxide emissions at regional scale. Long-term temperature data and the measureable urbanisation parameter plot ratio surrounding different auto weather stations were used to model the temperature changes for different degrees of urbanisation. Models representing daytime and nighttime respectively were developed based on these data, and the results suggested a logarithmic relationship between the rate of temperature change and plot ratio (degree of urbanisation). When the effects of global warming and present and future urbanisation are known, the actual rate of temperature increase at different locations across Hong Kong can be calculated. Future temperature maps can therefore be produced by applying the rate of increases to the current temperature maps. The current temperature patterns over the whole of Hong Kong were retrieved from two ASTER thermal images. One of the images was obtained in summer daytime while the other one was obtained at night. By a method of simple addition, the temperatures are projected towards 2039 in 10-year intervals. This research also studied the effects of future projected higher air temperatures on public health using the parameter of thermal comfort. Mortality is expected to rise as heat-related deaths may occur under a continuously hot environment during both day and night. The thermal comfort levels are also expected to decrease in the future because of the predicted hot and humid weather in Hong Kong.

Author	Ji, Luning
Title	Terminology extraction using contextual information
Department	Dept. of Computing
Year	2007

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Subject	Hong Kong Polytechnic University -- Dissertations. Chinese language -- Terms and phrases -- Data processing. Natural language processing (Computer science) Chinese language -- Data processing.
Degree	M.Phil.
Pages	xii, 146 leaves : ill. ; 30 cm.
Language	English
OneSearch	https://www.lib.polyu.edu.hk/bib/b2145953
URI:	http://theses.lib.polyu.edu.hk/handle/200/2233
Abstract	This work investigates different algorithms of automatic terminology extraction. The investigation considers two characteristics of terminology - unithood and termhood corresponding to two steps in terminology extraction, namely, term extraction and terminology verification. In the first step for term extraction, two statistic-based measurements considering the internal and contextual relationship are used to estimate the soundness of an extracted string pattern being a valid term. In the second step for terminology verification, window-based contextual information within a logical sentence is used. Two window-based approaches using on domain knowledge and syntax of the contextual information are proposed. After evaluating the merits and problems of each approach, a hybrid approach is designed to combine both the syntactic information and domain specific knowledge to verify the extracted candidate terms as terminology or not. Furthermore, a component-based composition algorithm is proposed to help verify the extracted terms as valid terminology. Experiments show that the hybrid approach can achieve significant improvement with the best F-measure, not only maintaining a good precision but also a good recall. Due to the special nature of Chinese, this work investigates details of the effect of word segmentation in terminology extraction through the comparisons of two preprocessing models - a character-based model and a word-based model. Limitations of segmentation and some feasible suggestions for dealing with these limitations are also provided. Furthermore, this work investigates methods to construct a core lexicon for a specific domain from an existing domain lexicon. The core lexicon contains the most fundamental terms used in a domain through which other terms in the domain can be constructed. Three different approaches considering four characteristics of core lexicon are proposed and implemented. Evaluations show that the automatic extracted core lexicon can have good coverage of the domain lexicon as well as being minimal with on redundant terms. The use of a core lexicon can reduce program runtime and memory usage in real applications.

Author	Yan, Jingya
Title	Terrain feature extraction at different levels
Department	Dept. of Land Surveying and Geo-Informatics
Year	2011

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Subject	Hong Kong Polytechnic University -- Dissertations Geomorphology -- Data processing
Degree	M.Sc.
Pages	viii, 62 leaves : ill. (chiefly col.) ; 30 cm.
OneSearch	https://www.lib.polyu.edu.hk/bib/b2412273
URI:	http://theses.lib.polyu.edu.hk/handle/200/5972
Abstract	Digital terrain analysis in three dimensions has been one of the most important research areas and applications in the geo-information sciences. Describing terrain surface in different levels not only helps to reduce the size of database and improve the efficiency, but also meets the various requirements of digital terrain analysis. The terrain morphological features play an important role in digital terrain analysis. This study aims to extract terrain features at different levels. The data of this project is one part of Port Navalo, in which one part of this area is over sea level and the other undersea. Because the landform is made up of various features, this study classifies the terrain morphological features into four levels, which are point level, line level, area level and shape level. The point level includes peak, pit and pass. The line level has ridge and channel. The area level has plane, which is used to build shape. The shape level contains uphill area, downhill area and flat area. In the segmentation, the slope value and slope direction are used to segment DTM in different levels. In order to represent terrain morphometric features in three dimensions, the feature areas should be merged as shapes. At last, the results of terrain morphometric features extraction have been discussed at the different levels of segmentation. Meanwhile, the partonomy relationship of terrain morphometric is used to classify landform. In addition, different kinds of data structure were used to store the data, attributions and relationships of DTM at the different levels. From the limited technique carried out in this study, some conclusions are made as follows: Based on the partonomy relationship, the three levels of terrain morphometric features can extract and represent terrain morphometric features in the DTM of three demensions. After comparing the terrain morphometric features at different levels of segmentation, it is easy to know the more details of terrain morphomertic features will be detected at the higher levels of segmentation. Meanwhile, based on the partonomy relationship, the different types of shape can be separated and represented clearly.

Author	Lee, Yuen-yin Rosa
Title	Testing of projection formula for the requirements of operating theatres in public hospitals of Hong Kong
Department	Multi-disciplinary Studies
Year	1997

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Subject	Public hospitals -- China -- Hong Kong Operating rooms Hong Kong Polytechnic University -- Dissertations
Degree	M.Sc.
Pages	x, 65, [28] leaves : ill. ; 30 cm
Language	English
OneSearch	https://www.lib.polyu.edu.hk/bib/b1397975
URI:	http://theses.lib.polyu.edu.hk/handle/200/3210
Abstract	There has been a growing discontent among users of operating theatres on insufficient theatre session time available for surgical operations in public hospitals of Hong Kong. Increasing dissatisfaction has also been shown by patients on the prolonged waiting time for surgical operation. As the methodology of planning theatre provisions has become questionable, a research study was initiated to device and test a projection formula for estimating requirements of operating theatres in public hospitals of Hong Kong. Data collected on the utilization and throughput of operating theatres in ten hospitals reveal substantial deviations in practices from the UK Planning Norms and findings of previous research studies carried out in UK. Three sets of planning ratios emerged from the research for the same variable "Average Number of Cases per Theatre Session", which has a significant impact on the estimation of workload capacity for an operating theatre. These three sets of ratios were therefore used to set up scenarios in order to test results of projected requirements using a projection formula identified in a previous research paper. The projection formula was based on the availability of surgical beds. Results of the test varied enormously and it was difficult to judge which sets of variables were appropriate for comparison with the existing provisions in order to assess the adequacy of provisions. The projected requirements based on planning ratios by specialty as revealed in the research study carried out in UK in 1986 and subsequently adopted by the Health Building Note 26 were eventually used as yardsticks for comparison. It was further recommended to base projections on an average length of bed-stay by specialty of the individual hospital and that the projection formula be modified by including a discounting factor to cater for those surgical patients who do not require surgical operation. Using the modified projection formula, it was able to identify a shortfall of theatre provision in four public hospitals.

Author	Ko, Koon-yuen
Title	Test methodologies for analogue cores of system-on-chip
Department	Dept. of Electronic and Information Engineering
Year	2003

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Subject	Hong Kong Polytechnic University -- Dissertations Systems on a chip -- Testing Integrated circuits -- Very large scale integration Metal oxide semiconductors, Complementary
Degree	M.Phil.
Pages	xii, 96 leaves : ill. ; 30 cm
Language	English
OneSearch	https://www.lib.polyu.edu.hk/bib/b1733079
URI:	http://theses.lib.polyu.edu.hk/handle/200/3219
Abstract	Three built-in self-test (BIST) techniques were developed during this research project. These testing techniques are: Weighed Sum of Selected Node Voltages (WSSNV), Summations of Cores' Test Output Voltages (SOCTOV) and Full Range Window Comparator (FRWC) BIST techniques. The first one is proposed for the effective testing of embedded analogue cores while the later two are proposed for that of the analogue portion of System-On-Chip (SOC). All these BIST techniques have the major advantages of high fault coverage, small hardware overhead and fast test application time. The WSSNV BIST technique makes use of the weighted sum of a pre-selected small set of circuit node voltages to detect faults. When compared with the voltage scan approach, the WSSNV BIST technique is verified to have higher fault coverage while at the same time hardware overhead is much less. It needs only an extra pin for testing output and a single DC stimulus is needed to feed at the primary input of the circuit (or core) under test (CUT). Studies have been carried out to apply the proposed BIST technique to an analogue active low pass filter; a mixed-signal threshold detector of a telephone ringer IC; and a simulated mathematical functional block of a SOC to verify its effectiveness and efficiency. Test architecture of the WSSNV BIST technique for embedded cores is also proposed. SOCTOV BIST technique is a unified BIST approach to SOC testing that is based on weighted and non-weighted sums of cores' test output voltages. It is developed in conjunction with the WSSNV BIST technique. Under test mode, all the test output voltages of the cores are summed together (weighted and non-weighted). By observing these weighted and non-weighted summing outputs and those known nominal values, the faulty condition of the SOC and the location of the faulty core can be uniquely identified. The WSSNV BIST technique provides high fault coverage for individual cores while the SOCTOV BIST technique provides a 100% fault diagnosis resolution for the location of faulty cores. FRWC BIST technique is based on Window Comparator of Cores' Test Output Voltages for the effective testing of embedded analogue cores. This BIST technique is also developed in conjunction with the WSSNV BIST technique. The resultant testing response is a binary bit stream which can be easily incorporated with the existing testing technique for the digital portion of the SOC such that a single digital Automatic Test Equipment (ATE) is all that required for the testing of a mixed-signal SOC. By reading the bit steam of the testing response, the health status of the SOC, location of the faulty core(s), and even the faults within the faulty core(s) can be identified. In contrast with the SOCTOV BIST technique, it has the major advantage of the capability to locate the unique faults (or equivalent fault sets) within the faulty core(s).

Author	Wong, Chuen-kau
Title	Text-independent speaker verification based on vector quantization
Department	Multi-disciplinary Studies Dept. of Electronic Engineering
Year	1998

[more]

Subject	Speech processing systems Automatic speech recognition Hong Kong Polytechnic University -- Dissertations
Degree	M.Sc.
Pages	iv, 52 leaves : ill. ; 30 cm
Language	English
OneSearch	https://www.lib.polyu.edu.hk/bib/b1436950
URI:	http://theses.lib.polyu.edu.hk/handle/200/322
Abstract	This thesis implements text-independent speaker verification experiments for clean and telephone speech based on vector quantization. The well-known speech databases, TIMIT and NTIMIT, are used. 12th-order LPC-derived cepstrum coefficients are extracted from 50% overlapping frames of speech signal and are used as input feature vectors. Each speaker in the speaker set is modeled by a personalized VQ codebook and is associated with a decision threshold. Each speaker's threshold is estimated by the distributions of the intraspeaker and interspeaker distances, which are assumed Gaussian. All thresholds are then approximated by a linear regression line. Cepstral distance measure is naturally chosen for comparing the similarity of two spectral vectors. Full search Generalized Lloyd algorithm with Binary Splitting method is used to train the codebooks. The codebook sizes are varied from 16 to 128. The effects of different codebook sizes on system performance are demonstrated. The first set of experimental results show that codebook size of 64 performs the best for both clean and telephone speech. Average verification error rates of 1.01% and 22.16% have been achieved respectively for clean and telephone speech. The second experiment evaluates the effects of using the index-weighted cepstral distance measure on the verification performance. As expected, better results are obtained for high quality speech. Furthermore, codebook size of 128 produces a fairly low average error rate of 0.61% but no improvement is observed for noisy channel. The final experiment demonstrates the effect of using combined codebooks on the system performance. In addition to the instantaneous VQ codebooks, a transitional VQ codebook, which contains delta-cepstral vectors as its codebook entries, is added to model each speaker. The relative contribution of instantaneous and transitional spectral information is investigated. The optimal combination factors for codebook sizes of 64 and 128 are found empirically. An average error rate of slightly less than 1% for codebook size of 64 has been obtained for clean speech but poor results for telephone speech still exist. All these lead to a conclusion that pre-processing of telephone speech signal for removing the noise and channel variations is necessary.

Author	Wong, Chi-bun
Title	A text-independent speaker verification system based on Gaussian mixture speaker models
Department	Multi-disciplinary Studies Dept. of Electronic Engineering
Year	1998

[more]

Subject	Speech processing systems Automatic speech recognition Hong Kong Polytechnic University -- Dissertations
Degree	M.Sc.
Pages	42, [16] leaves : ill. ; 30 cm
Language	English
OneSearch	https://www.lib.polyu.edu.hk/bib/b1425846
URI:	http://theses.lib.polyu.edu.hk/handle/200/823
Abstract	Because of the growing demand and popularity of 24-hour telephone banking services, security of financial transactions on the public telephone network becomes an important issue. Since different speakers have different speech features, the verification of the speakers is believed to be a possible way to enhance the security of these transactions. This project proposes to use Gaussian Mixture Models (GMMs) for speaker verification. Basically, GMM adopts an implicit segmentation approach. It provides a probabilistic model of the underlying sounds of a person voice, but it does not impose any Markovian constraints on the sound classes. Besides, it can be integrated with a statistical background noise model for noise robustness. Furthermore, it models speaker identity based on two interpretations. Firstly, the Gaussian components are used to represent the spectral shapes of phonetic sounds, which characterise a person voice. Secondly, by modeling the underlying acoustic classes, it is better to model the short-term variations of a person voice, allowing a high verification performance for short utterances. In this project, GMMs with diagonal covariance matrices have been built and text-independent speaker verification experiments have been performed. All speech samples were taken from the dialect region 2 of the DARPA TIMIT speech corpus. In order to compare the performance of the Gaussian Mixture models between a noisy and a noise free environment, both TIMIT (noise free speech database) and NTIMIT (noisy telephone bandwidth speech database) were used in the experiments. The objective of the experiments is to evaluate the performance of the GMM models in terms of the error rates of the speakers verification. Basically, it can be divided into three steps. Initially, 20 speakers have been trained by using the SA and SX sentence sets of the TIMIT and NTIMIT corpuses. Next, a threshold is calculated which is used to determine whether to accept or to reject a claimant when his feature vectors are presented to the speaker GMM. Finally, all feature vectors derived from the SI sentence set of 36 impostors are input into the GMMs to calculate the individual false acceptance rate and the overall false acceptance rate. The results show that, as far as TIMIT database is concerned, the verification error rate decreases when the number of Gaussian components increases from 8 to 64. The lowest achievable error rate is 4.13%. As for NTIMIT database, the verification error rate decreases when the number of Gaussian components increases from 8 to 40, However, the error rate increases when the number of Gaussian components is greater than 40. The lowest achievable error rate AErr is 10.96%. From the above results, it can be concluded that GMMs is more suitable for applying at a noise free environment and it can achieve a very low verification error rate. If GMMs is applied at a noisy environment, a better preprocessing technique is essential. Moreover, the verification result shows that Gaussian mixture models are speaker and impostor dependent. It may be owing to the fact that some speakers or impostors have dependent components. To achieve a better recognition result, it is found that the diagonal covariance matrices can be replaced by the full covariance matrices. In addition, the clustering size analysis shows that more than 70% of Gaussian components is not well trained, therefore they can be removed, resulting in less parameters and a faster calculation.

Author	Chan, San Sheung
Title	TFE3, a novel diagnostic marker for solid pseudopapillary tumor of pancreas
Department	Dept. of Health Technology and Informatics
Year	2014

[more]

Subject	Pancreas -- Tumors -- Diagnosis. Genetic markers Hong Kong Polytechnic University -- Dissertations
Degree	M.Sc.
Pages	xii, 71 leaves : color illustrations ; 30 cm
OneSearch	https://www.lib.polyu.edu.hk/bib/b2759012
URI:	http://theses.lib.polyu.edu.hk/handle/200/7592
Abstract	Solid pseudopapillary tumor of pancreas (SPN) is an uncommon low grade malignant neoplasm mainly affecting young female patients. Its etiology and pathogenesis are still not fully known. The morphology of SPN is similar to some other pancreatic neoplasms such some pancreatic ductal adenocarcinoma (PDAC) and islet cell tumor (ICT). This causes difficulty in their differential diagnosis. Transcription factor for immunoglobulin heavy chain enhancer 3 (TFE3) is a transcription factor belonging to the helix-loop-helix family. Its gene is located on the short arm of chromosome X with the notation of Xp11.2. Its function is diverse including activation of glycogen and protein synthesis, cell growth, cell differentiation and T-cell-dependent antibody responses. Clinically, TFE3 translocation is found in certain types of neoplasm. They are Renal Xp11 translocation carcinoma (Xp11RCC), alveolar soft part sarcoma, perivascular epithelioid cell tumor (PEComa), and epithelioid hemangioendothelioma. The involved fusion partner genes include PRCC gene, CLTC gene, PSF gene, ASPSCR1 gene, NONO gene and YAP1 gene. We noticed that there is some morphology resemblance of SPN to TFE3 associated renal cell carcinoma. We then performed a retrospective study on 19 archived FFPE samples of SPN (n=9), ICT (n=5) and PDAC (n=5). In this study, immunohistochemistry (IHC) and RT-PCR were used to detect the expression of TFE3 and compared the results with the clinicopathological features. The fluorescence in situ hybridization (FISH) with dual colour break apart probe was used to detect translocation. From the results, the morphology features in Xp11RCC, namely rosette structure with hyalinized stromal core were identified in the H&E of the SPN cases. In IHC part, most SPN cases (~78%) scored positive (nuclear staining), whereas all ICT and PDAC cases scored negative. But, there were no break apart signal in FISH was detected for those SPN cases. For RT-PCR, we compared TFE3 mRNA expression in SPN and their respective normal pancreatic tissue. Only five cases were successful while others did not give any result due to not enough tissue samples. Although 4 cases showed slightly increase, the number of case were too small for any statistical analysis. In conclude, this study demonstrated the overexpression of TFE3 in SPN by IHC. There was no correlation between this with the clinicopathological features. Also, no translocation was detected for that overexpression. This suggested other mutation or mechanism is involved. On the other hand, ICT and PDAC showed negative in TFE3 IHC. This can aid the differential diagnosis between them with SPN. Moreover, the overexpression of TFE3 indicated that it is an important factor in the pathogenesis of SPN, and, it may be a potential therapeutic target.

Author	Ho, Kam-wa
Title	The fabrication and characterization of BiFeO₃nanotubes
Department	Dept. of Applied Physics
Year	2009

[more]

Subject	Hong Kong Polytechnic University -- Dissertations Nanotubes Bismuth Ferrite
Degree	M.Phil.
Pages	75 leaves : ill. ; 31 cm.
OneSearch	https://www.lib.polyu.edu.hk/bib/b2342998
URI:	http://theses.lib.polyu.edu.hk/handle/200/5695
Abstract	Bismuth ferrite (BiFeO₃) nanotubes were fabricated using the sol-gel nano-channel alumina (NCA) template method. The resulting nanotubes were about 60 μm in length and 200 nm in diameter. Different fabrication parameters were applied systematically to different BiFeO₃samples in order to assess the influence of the most effective parameters on the crystallization of the nanotubes. Extended crystallization, accompanied by reduction in second-phases within the nanotubes was the main goal of the studies. The parameters used in the fabrication of the nanotubes, included: different annealing temperatures, different annealing temperatures times, template thickness, precursor solution concentration and composition. The characterization of the structure, microstructure and local composition of the nanotubes were carried out using transmission electron microscopy (TEM) and X-ray energy dispersive microanalysis (EDS). Scanning electron microscopy (SEM) was used extensively to study the morphology of the resulting nanotubes. Investigations showed that the majority of the individual nanotubes were multi-phase, non-stoichiometric polycrystalline structure and primarily composed of numerous nano-particles imbedded within each nanotube. It was established that the major parameters that influenced the crystallization of the nanotubes or the nano-particles embedded within the nanotubes, were the annealing time, as well as the concentration of the precursor solution. In addition, the crystallization of the nanotubes was markedly dependent on the annealing temperature applied to the nanotubes. Higher solution concentration was the secondary factor that influenced the crystallization of the nanotubes. The Piezo-Force Microscopy (PFM) technique was used to measure the properties of the nanotubes with very limited success. Using PFM, major difficulties were encountered in measuring the electrical properties of the nanotubes accurately. The difficulty was attributed mainly to excessively small tube size, as well as the inability to adhere proper electrical contacts to a nanotube. Isolating an individual and complete nanotube from the template proved extremely difficult.

Author	Lo, Shuk-ting Doris
Title	The theme park experience : its nature, antecedents and consequences
Department	School of Hotel and Tourism Management
Year	2008

[more]

Subject	Hong Kong Polytechnic University -- Dissertations. Amusement parks. Consumer satisfaction.
Degree	M.Phil.
Pages	x, 210 p. : ill. ; 30 cm.
Language	English
OneSearch	https://www.lib.polyu.edu.hk/bib/b2233732
URI:	http://theses.lib.polyu.edu.hk/handle/200/1255
Abstract	Customer experience has become a new measure of success in the theme park industry. With the increase in discretionary income and travelling opportunities, residents and tourists have become more demanding in their expectations of theme park performance. They want theme parks at which they can have a good time with friends and relatives and which evoke positive emotional feelings. However, the intricacies of visitor experience have been addressed in few theme park studies. Using quality of experience and affect to measure theme park experience, this study attempts to explore the psychological nature of the theme park experience, and to examine its antecedents and consequences. A structural equation model was used to test visitor experience of the Hong Kong Disneyland. The model included three exogenous variables - audience, actors and service setting - that are three components of the Services Theatre model, and four endogenous variables - quality of experience, affect, overall satisfaction and behavioural intention. Interviews with 475 Hong Kong visitors were carried out at the exit gate of Hong Kong Disneyland. Two scales were developed for measuring theme park performance and experience. Three experience dimensions, "enjoyment and fun", "learning, fulfilment and novelty" and "relaxation and relationship", were used to measure the quality of visitor experience at the theme park. All the scales were pre-tested and refined using exploratory and confirmatory factor analysis. The findings revealed that the proposed model fit the observed data well, with acceptable model fit indices. Theme park experience was confirmed to be a significant mediator between theme park performance and overall satisfaction. Park setting was found to be the theme park component that most affected the quality of visitor experience and emotional feelings (i.e., theme park experience). In addition, the behaviour of other visitors also had a considerable effect on the emotional feelings of in-park visitors. Given that the theme park experience of visitors plays a significant role in affecting their satisfaction and their intention to return, theme park operators need not only to put efforts into improving theme park services, but also to understand and carefully manage the theme park experience.

Author	Zhao, Le
Title	Theoretical analysis of effects caused by mixing proportion on plume potential
Department	Dept. of Building Services Engineering
Year	2011

[more]

Subject	Plumes (Fluid dynamics) Cooling towers -- Environmental aspects. Atmospheric diffusion. Hong Kong Polytechnic University -- Dissertations
Degree	M.Eng.
Pages	ix, 74 leaves : ill. (chiefly col.) ; 30 cm.
Language	English
OneSearch	https://www.lib.polyu.edu.hk/bib/b2451600
URI:	http://theses.lib.polyu.edu.hk/handle/200/6398
Abstract	Visible plume from evaporative cooling towers has been a hot spot issue in HVAC (Heating ventilation and air conditioning) field for many years. People show large concern about how to eliminate the plume as it could result in misconception of a fire accident or a hazardous pollutant for local people in highly dense city. Studies conducted on this topic showed different results and many approaches have been proposed to solve this problem. A study by Xinhua Xu et al investigated the reason for plume occurrence and proposed two approaches to control or eliminate it accordingly. This study aimed to investigate this topic by analyzing mixing processes with different mixing proportions and how the mixing proportion could have effects on plume potential. Analysis based on theoretical calculations was applied to analyze the mixing process of ambient air and exhaust air from cooling tower under some typical weather conditions. And the plume potential of those mixing processes is also examined. The result indicates that in general, the plume potential increases with the growth of relative humidity of ambient air. With the increase of mixing proportion of ambient air in mixing process, the increasing degree becomes larger and larger gradually. However, the plume potential decreases with the growth of ambient air temperature, the decreasing degree seems to be almost the same under different mixing proportions. When the relative humidity of ambient air is larger than that of exhaust air from cooling tower; the plume potential increases with the growth of proportion of ambient air in mixing process in general When the relative humidity of ambient air is equal to that of exhaust air from cooling tower, the plume potential generally increases first and then decreases gradually with the increase of proportion of ambient air in mixing process. When the relative humidity of ambient air is smaller than that of exhaust air from cooling tower, the plume potential has a general decrease trend with the growth of proportion of ambient air in mixing process.

Author	Chow, Ka Chun Ronald
Title	Theoretical chemical kinetics of atmospheric reactions with near-zero and negative barriers
Department	Dept. of Applied Biology and Chemical Technology
Year	2018

[more]

Subject	Hong Kong Polytechnic University -- Dissertations Chemical kinetics Chemical reactions Chemical engineering
Degree	M.Phil.
Pages	xx, 208 pages : color illustrations
Language	English
OneSearch	https://www.lib.polyu.edu.hk/bib/99102209
URI:	http://theses.lib.polyu.edu.hk/handle/200/9380
Abstract	The atmosphere consists of many gases and radicals and many reactions could occur, thereby forming a very dynamic system. Due to the unstable nature of radicals, they are short-lived which make experimental studies difficult. Moreover, reactions involving radicals (such as radical-radical reactions) have low or negative barriers. The life time of these radicals short, which make them and their reactions difficult to observe. Furthermore, some conditions can be challenging to achieve in laboratory, such as very high or very low temperature and/or pressure, or the complete desirable ranges. In view of these experimental challenges of gas phase studies, theoretical methods (ab initio (wavefunction-based) methods, density functional theory (DFT), and the transition state theory (TST)) provide alternative ways to study gas phase reactions without subject to the aforementioned difficulties, especially for reactions involving radicals. This work aims to establish reliable and practical methods to calculate rate coefficients for chemical reactions with low or negative barriers, which involves the investigation of the interrelationships between the rate coefficients, the reaction surface and the computed barrier heights. In particular, two atmospherically important reactions were studied computationally, namely the CH3C(O)OCH3 + Cl reaction and the BrO + HO2 reaction. The former is a reaction with a low barrier while the major channel of the latter is a reaction with a negative barrier. Rate coefficient calculations showed that one vibrational mode changed dramatically along the reaction coordinate, leading to a dramatic change of the zero-point energy (ΔZPE) along the reaction coordinate. Consequently, large variational effects resulted for reactions with flat and very flat reaction surfaces, which were characterized by small classical adiabatic ground-state transmission factors (CAG factors). This approach is effective in compensating for the deficiency of the TST method. The results also showed that the locations of the maxima of the ΔG curves at certain temperatures were a bit away from the saddle point at a negative reaction coordinate (i.e. in the reactant side), especially for reactions with low and negative barriers. This indicated that the choice of the intrinsic reaction coordinate in rate coefficient calculations had to cover the maximum of a ΔG curve in order to obtain accurate rate coefficients. It was also found that the pre-exponential entropic terms, which were computed using the vibrational frequencies and geometrical parameters, had significant effects on the computed rate coefficients, especially for chemical reactions with low and negative barriers. Thus, in addition to the accuracies of the computed barrier heights, the accuracies of the computed harmonic frequencies and geometries along the reaction coordinate also play crucial roles as they in part determined the accuracies of rate coefficients. This work has also provided the computed barrier heights, reaction mechanisms, reaction enthalpies and rate coefficients of the two reactions, so that they can be used for further kinetic modeling.

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