http://dspace.fsktm.um.edu.my/handle/1812/8 Search the Channel search http://dspace.fsktm.um.edu.my/simple-search http://dspace.fsktm.um.edu.my/handle/1812/788 Title: The reproductive biology and ecology of Johannesteijsmannia Lanceolata J. Dransf. (Arecaceae) <br/> <br/>Authors: Chan, Yoke Mui <br/> <br/>Abstract: Johannesteijsmannia lanceolata is a rare species endemic to Peninsular Malaysia, and is threatened by deforestation and seed harvesting for the ornamental trade. Before proper conservation strategies can be implemented for this species, the understanding of its reproductive biology and ecology is crucial for the assessment and prediction of the population viability under such threats. Thus, this thesis aimed to investigate its phenology, breeding system, embryology, and its distribution across topography (ridge, slope and valley) in a 3.2 ha plot in the Angsi Forest Reserve, Negeri Sembilan. Possible conservation measures were discussed. The wild population showed seasonal flowering, while the cultivated population exhibited steady state flowering. Flowering was weakly correlated with rainfall. The reproductive cycle from flowering to fruiting took 14–15 months. Flowers were homogamous, with peak anthesis from 0730–1100 hours, while the stigma was receptive for only one day. Potential pollinators were stingless bees (Trigona sp.) and small flies (Phoridae and Cecidomyiidae). The palm was facultatively selfing with very low fruit set (<0.05 %). The pollen was elliptic, monosulcate with a smooth exine, and lost its viability after one day. The microspore tetrads were tetrahedral (rarely isobilateral), and formed by simultaneous cytokinesis. The ovule was anatropous, crassinucellate and bitegmic. Twin archesporia and T-shaped megaspore tetrads were rare. The embryo sac development was of the monosporic, 8-nucleate Polygonum type. The distribution of the palm differed across topography, with the density highest in valleys (65 individual ha-1), and is likely influenced by seed recruitment, interspecies competition and topographic features. In-situ conservation and a sustainable seed harvesting regime of Johannesteijsmannia lanceolata are strongly recommended, because the species is narrowly endemic, and has a long reproductive cycle with very low fruit set (2–6 mature fruits per fruiting season). ABSTRAK Johannesteijsmannia lanceolata adalah spesies jarang dan endemik di Semenanjung Malaysia, yang menghadapi ancaman daripada pembukaan hutan dan pengutipan biji benih untuk perdagangan tumbuhan hiasan. Sebelum kita dapat melaksanakan strategi pemuliharaan yang sesuai untuk spesies ini, pemahaman mengenai biologi pembiakan dan ekologi palma ini adalah mustahak bagi menilai dan meramal kemandirian populasi di bawah ancaman tersebut. Maka, tesis ini bertujuan mengkaji fenologi, sistem pembiakan, embriologi dan taburan spesies tersebut melintang topografi (rabung, cerun, lembah) di plot kajian 3.2 ha di Hutan Rizab Angsi, Negeri Sembilan. Saranan-saranan pemuliharaan juga dibincangkan. Populasi liar berbunga secara bermusim, manakala populasi yang di tanam berbunga secara berterusan. Korelasi pembungaan dengan jumlah hujan adalah lemah. Kitar pembiakan dari bunga ke buah mengambil masa 14–15 bulan. Bunga adalah homogami, dengan kemuncak antesis dari jam 0730–1100, manakala stigma kekal reseptif selama satu hari sahaja. Kelulut (Trigona sp.) dan lalat kecil dari keluarga Phoridae and Cecidomyiidae berkemungkinan besar adalah agen pendebungaan. Palma tersebut berupaya kacuk sendiri dan kacuk luar dengan penghasilan buah matang yang sangat rendah (<0.05%). Debunga adalah eliptik, monosulkat dengan eksin licin, dan hilang kemandiriannya selepas satu hari. Tetrad mikrospora adalah tetrahedral (jarang isobilateral), dibentuk oleh sitokinesis serentak. Ovul adalah anatropus, krasinuselat dan bitegmik. Arkesporia kembar dan tetrad megaspora berbentuk T jarang ditemui. Perkembangan pundi embrio adalah jenis monosporik Polygonum. Taburan palma tersebut adalah berbeza apabila melintang topografi, dengan kepadatan maksima di lembah (65 individu ha-1), dan mungkin dipengaruhi oleh rekrut biji benih, persaingan interspesies dan ciri-ciri topografi. Pemuliharaan in-situ dan rejim pengutipan biji benih Johannesteijsmannia lanceolata secara lestari adalah sangat disarankan, kerana spesies tersebut adalah endemik, dan mempunyai tempoh kitar pembiakan yang panjang dengan penghasilan buah matang yang sangat rendah (2-6 biji per musim buah). <br/> <br/>Description: Dissertation -- Faculty of Science, University of Malaya, 2009. Sun, 01 Mar 2009 00:00:00 GMT http://dspace.fsktm.um.edu.my/handle/1812/787 Title: SOA-based fiber ring laser <br/> <br/>Authors: Abdul Hadi Sulaiman <br/> <br/>Abstract: ABSTRACT This dissertation investigates the generation of laser wavelength using a semiconductor optical amplifier (SOA) in conjunction with an array waveguide grating (AWG) and a fiber bragg grating (FBG) in a ring configuration system. The experimental system utilizing the FBG produced a single laser wavelength with a peak power of -27.45 dBm and this value increases to -18.40 dBm as a modulator is applied in the configuration. As the AWG is utilized in the ring configuration, a maximum of four laser wavelengths at an equivalent peak power can be produced. A system with two-cascaded SOAs is configured, as the peak power is higher and the spectral width is wider. A dual wavelength ring laser system is designed and we obtained a peak power of -17.03 dBm and -14.95 dBm at wavelengths of 1530.2 nm and 1532.6 nm respectively. A quad wavelength ring laser is also demonstrated which capable of generating four laser wavelengths at 1531.0 nm, 1533.3 nm, 1535.7 nm and 1538.0 nm, with an equivalent peak power of -20 dBm and channel spacing of 0.24 nm. The design is upgraded by the addition of another SOA and it is found that the average peak power and lasing bandwidth is increased as well. The multiple wavelength ring laser against time showed a stable operation at 80 minutes with negligible fluctuations in the laser wavelength. The demonstrated laser configurations have the advantage of stable multiple wavelengths, a simple and compact design as well as their potential in various applications of sensors and DWDM system. ABSTRAK Dissertasi ini mengkaji penghasilan saluran laser menggunakan pengganda optik semikonduktor (SOA) bersama-sama dengan susunan jeriji yang memandu gelombang (AWG) dan jeriji Bragg gentian optik (FBG) di dalam sistem konfigurasi gelang. Sistem eksperimen menggunakan FBG menghasilkan satu saluran laser dengan kuasa puncak - 27.45 dBm dan nilai ini meningkat kepada -18.40 dBm apabila sebuah pemodulasi dimasukkan ke dalam konfigurasi. Apabila AWG digunakan di dalam konfigurasi gelang, maksimum empat saluran laser pada kuasa puncak yang sama boleh terhasil. Sistem dengan dua SOA yang disusun secara sesiri telah dikonfigurasi dimana kuasa puncak lebih tinggi dan keluasan spektral lebih luas. Satu sistem laser gelang dua saluran telah direka dimana kita telah mendapat kuasa puncak -17.03 dBm pada saluran 1530.2 nm dan kuasa puncak -14.95 dBm pada saluran 1532.6 nm. Laser gelang empat saluran juga telah ditunjukkan dimana ianya berupaya menghasilkan empat saluran laser pada panjang gelombang 1531.0 nm, 1533.3 nm, 1535.7 nm and 1538.0 nm dengan kuasa puncak yang sama pada -20 dBm dan selang saluran 0.24 nm. Rekaan tersebut telah ditingkatkan dengan penambahan satu lagi SOA dan didapati kuasa puncak purata dan jalur lebar saluran masing-masing meningkat. Laser gelang saluran berganda melawan masa menunjukkan operasi yang dijalankan selama 80 minit ini adalah stabil dengan naik-turun yang boleh diabaikan pada saluran laser. Konfigurasi-konfigurasi laser yang telah ditunjukkan mempunyai kelebihan pada saluran bergandanya yang stabil, rekaannya yang mudah serta padat dan juga potensinya pada pelbagai aplikasiaplikasi pengesan dan sistem DWDM. <br/> <br/>Description: Dissertation -- Faculty of Science, University of Malaya, 2009. Thu, 01 Jan 2009 00:00:00 GMT http://dspace.fsktm.um.edu.my/handle/1812/731 Title: Optimization and characterization of 130 NM CMOS transistor design using TCAD simulation <br/> <br/>Authors: Hani Noorashiqin Abd. Majid <br/> <br/>Abstract: ABSTRACT Microelectronic device manufacture encompasses the fabrication, testing and simulation, of structures utilized in a variety of application specific integrated circuits. The fabrication of transistors, traditionally from elemental silicon wafer is conducted in a clean room environment utilizing various types of equipment. Process simulation is a critical element in facilitating the optimization of fabrication stages, confirming test results and theoretical models and providing physical insight into structural operation. TSUPREM-4 and MEDICI are two simulators that had been calibrated and used in this work. As device sizes are scaled down, novel structures are proposed such as halo (pocket), lightly doped drain (LDD) and source/drain process. In order to characterize and optimize Silterra 130 nm CMOS transistor design, TCAD simulation is done in this work and the results is compared with measured data and was verified to be in the Silterra specification range. Various doses, implant energies and tilt angle is used to upgrade the transistor performance, reduce the short channel effect and increase the transistor lifetime. Halo implant, lightly doped drain (LDD) implant and source/drain (S/D) implant is the three drain engineering structure to be characterized in this work. It is found that at certain dose, implant energy and tilt angle, the best saturation drain current, Idsat and threshold voltage, Vt that can match the specification target for NMOS and PMOS transistor can be achieved. It is also proved in this work that by using process and device simulator, the correct process can be predicted and the physical insight of the structure such as current flow lines and doping concentrations can be further analyzed. ABSTRAK Pengeluaran peranti mikroelektronik merangkumi pembuatan, menguji dan simulasi, struktur-struktur yang digunakan dalam pelbagai aplikasi khusus litar-litar bersepadu. Pembuatan transistor, terdiri daripada wafer silikon asas dikendalikan dalam satu persekitaran tempat bersih dengan menggunakan pelbagai jenis peralatan. Proses simulasi adalah satu unsur penting yang membantu dalam mengoptimumkan peringkatperingkat pembuatan, mengesahkan hasil percubaan dan model-model teori dan menyediakan fahaman secara fizikal ke atas operasi struktur. TSUPREM-4 dan MEDICI adalah dua jenis simulator yang telah ditentukurkan dan digunakan dalam tugas ini. Setelah saiz-saiz peranti telah diturunkan, struktur-struktur novel telah dicadangkan seperti proses implant halo ‘halo (pocket)’, ‘lightly doped drain (LDD)’ dan proses ‘source/drain’. Dalam peringkat untuk mencirikan dan mengoptimumkan rekabentuk transistor CMOS Silterra 130 nm, simulasi TCAD telah dijalankan dalam projek ini dan hasil-hasilnya telah dibandingkan dengan data yang telah diukur dan telah disahkan ia berada di dalam julat spesifikasi Silterra. Pelbagai dos, tenaga mengimplan dan sudut mengimplan digunakan untuk menaiktaraf prestasi transistor, mengurangkan kesan saluran pendek dan menambah jangka hayat transistor. Implan halo, ‘lightly doped drain (LDD)’ dan proses ‘source/drain’ adalah tiga jenis struktur kejuruteraan parit yang akan dikaji dalam kerja ini. Didapati, dengan dos tertentu, tenaga implan dan sudut condong implan, arus parit tepu, Idsat dan voltan ambang, Vt yang terbaik dapat menepati sasaran spesifikasi bagi transistor NMOS dan PMOS. Dalam kerja ini ia dapat dibuktikan bahawa dengan menggunakan proses dan alat simulator, proses yang menepati spesifikasi dapat diramal dan struktur dalaman seperti aliran arus dan kepekatan pengedopan seterusnya dapat dianalisa. <br/> <br/>Description: Dissertation -- Faculty of Science, University of Malaya, 2007. Mon, 01 Jan 2007 00:00:00 GMT http://dspace.fsktm.um.edu.my/handle/1812/620 Title: Comparison of esterases between life stages and sexes of resistant and susceptible strains of vector mosquitoes <br/> <br/>Authors: Selvi Subramaniam <br/> <br/>Description: Dissertation (M.Sc -- Faculty Science, University of Malaya, 2009. Wed, 01 Jul 2009 00:00:00 GMT http://dspace.fsktm.um.edu.my/handle/1812/607 Title: Rigid and flexible polyurethane foams production from palm oil-based Polyol <br/> <br/>Authors: Lee, Choy Sin <br/> <br/>Abstract: Polyurethane foams are amongst the most important class of specialty polymers. It can be divided into three major classes, namely rigid, semi-rigid and flexible polyurethane foams. According to M.L. Kerman (2005), the global polyurethane market in 2004 showed that flexible polyurethane foams contributed 47% of the market share, followed by 26% of rigid foams, and 27% of other applications in coatings, adhesives, sealants and elastomers (CASE), binders, foundry and machinery. Rigid polyurethane foams are particularly useful in the construction industries as they are used as components such as polymeric concretes, insulating materials and sealants. In addition, flexible polyurethane foams are as cushion in the furniture, bedding and automotive industries. Conventionally, polyol is mainly derived from petrochemicals. They play an important role in the polyurethane industry. However, in view of the environmental and sustainability issues, the use of vegetable oil-derived polyol can serve as a substitute in the polyurethane industry. Malaysia is one of the major producers of palm oils. Therefore, the utilization of palm oils in the synthesis of polyols for both rigid and flexible polyurethane foams was initiated in this study. In this study, epoxidized diethanolamides was produced as a new type of polyol by reacting diethanolamine (DEA) with various ratio of Epoxidized Palm Olein (EPOo) to Refined Bleached Deodorized Palm Kernel Olein (RBDPKOo). The products were further reacted with diisocyanate and catalyzed by AlCl3-THF to produce rigid polyurethane. Concurrent with the production of rigid polyurethane, two minor important side-products oxazolidones and isocyanurates were produced to give significantly a better quality of rigid polyurethane. This is due to epoxidized diethanolamides with higher oxirane oxygen contents (OOC) that produced rigid polyurethane foams of higher compression strength (338.8 kPa), close cell contents (97.95%) and lower thermal conductivity (0.0288 w/m.K). In this work, only epoxides in diethanolamide polyol was reacted with isocyanate that resulted in the formation of hard segments oxazolidone and isocyanurate in the rigid polyurethane and this improved the compression strength and close cell contents of the foam. In addition, higher OOC in diethanolamides also gave better dimensional stability to the rigid foam that was conditioned at 70 °C and -25 °C. Apart from mechanical improvements, epoxides that were retained in diethanolamide structure also improved the thermal stability of the rigid foam. Thermogravimetric Analysis (TGA) was recorded with higher decomposition temperature for foam produced with higher OOC diethanolamides. Formation of oxazolidones in the urethane backbones and isocyanurates exhibited good-heat resistance that significantly enhanced the thermal stability of the foams. Index 1.40 was determined to be the most suitable isocyanate index when the polyurethane foam were altered by isocyanate index from 0.90 to 1.10. It produced non-brittle rigid foam with the lowest thermal conductivity (0.0288 w/m.K) and the highest close cell contents (97.95%) while maintaining moderate compression strength (338.8 KPa). One type of polyester polyol is synthesized by ring opening of synthetic epoxidized resins with dicarboxylic acids. Conventionally, the epoxides that used in the preparation of polyester polyol were ethylene oxide, propylene oxide, phenylglycidyl ether (PGE), diglycidyl ether of bisphenol A (DGEBA) and 3-phenoxy-1,2-epoxypropane. The versatile polyols were used mainly as fat-based non-ionic detergent, surface active agent, thermoplastic, paper coating resin and material for radiation shielding materials, curable printing ink and as coating. Therefore, in the second part of this study polyester polyol was prepared by using EPOo as the starting material instead of the synthetic epoxy resin. The polyester polyol was synthesized by reacting EPOo with different carbon chain length of aliphatic dicarboxylic acids ranging from C6 to C12. This produced a new type of polyol. The new polyol was mixed thoroughly with 50% of commercial polyol and they were reacted with toluene diisocyanate (TDI) to produce flexible polyurethane foam. The flexibility of the polyurethane foam was due mainly to the high average molecular weight and hydroxyl functional groups that were attached to the carbon chain of the polyols. Longer carbon chain in dicarboxylic acid was found to be more reactive than the shorter chain, which resulted in lower OOC (0.42%) of polyol mixture with bigger average molecular weight (Mw= 10526 g/mol). However, it also produced polyester polyol with higher hydroxyl value (103.6 mg KOH/g sample), viscosity (9755.21 cP at 25 °C, 4222.41 cP at 40°C), cloud point (20.04 °C) and pour point (12.00 °C) when compared to shorter carbon chain of dicarboxylic acid. Longer carbon chain of dicarboxylic acid used to produce polyester polyol resulted in the improvement of the foam properties such as hysteresis (22.76%), elongation at break (181.1 %) and thermal stability. The temperature of the decomposition peak (Tdec) of polyurethane as shown in DSC analysis and the decomposition temperatures of 10%, 50% and 90% of foam weight loss in TG analysis were increased. But, polyol synthesized from shorter carbon chain of dicarboxylic acid produced foam with better tensile stress and tear resistant ability. Isocyanate index 1.00 was selected as the optimal index as it produced flexible foam with the lowest hysteresis (23.64%), highest tensile stress (138.0%) and the best tear resistant ability (0.2382 N/mm). Flexible foam produced from higher isocyanate index was determined to be more stable thermally. However, alteration of isocyanate index did not produce foam with significant changes in terms of cellular structure, but the open cell contents of the foams prepared with different isocyanate index and polyester polyol were in a satisfactory range of 95-97%. Based on physical evaluation, 2 g of water content was the most suitable amount to be used in the production of flexible foams in comparison to 3 g and 4 g of water contents. This was mainly because 2 g of water content produced foam with the lowest hysteresis, highest elongation at break and better tear resistance ability. Nevertheless, increment of water content increased the foams’ open cell contents from 95% to 98% due to the emission of carbon dioxide generated from the reaction of isocyanate with water to form hard segment urea. Therefore, foam with higher content of urea that produced by higher water content as blowing agent were determined to be more stable thermally. Optical microscope also recorded open cells in various pentagon sizes that produced cells of bigger sizes in higher water content produced foam whereas lower water content produced foams with smaller cells in size and also more uniform in structure. ABSTRAK Busa poliuretana merupakan salah satu jenis polimer yang penting dan boleh turut dibahagikan kepada tiga kelas utama, iaitu, busa keras, semi-keras dan fleksibel. Menurut kepada M.L. Kerman (2005), pasaran poliuretana dunia pada 2004 menunjukkan bahawa poliuretane fleksibel menyumbang 47%, diikuti oleh 26% busa keras dan 27% aplikasi lain. Busa keras sangat berguna dalam industri pembinaan iaitu sebagai bahan konkrit, penebat haba dan sebagainya. Di samping, poliuretana fleksibel iaitu kusyen digunakan dalam industri perabot. Kebanyakan poliol yang memainkan peranan utama dalam industri poliuretana adalah dihasilkan dari bahan kimia petrol. Memandangkan isu pemuliharaan dan persekitaran yang mustahak, penggunaan poliol yang berasaskan minyak sayur amat dipentingkan. Malaysia merupakan salah sebuah negara penghasilan minyak kelapa sawit yang utama, oleh demikian, kerja penyelidik ini menggunakan minyak kelapa sawit untuk mensintesiskan dua jenis poliol yang boleh digunakan dalam pembuatan busa keras dan busa fleksibel. Poliol dietanolamida dengan kumpulan epoksi telah dihasilkan sebagai sejenis poliol baru di mana dietanolamina ditindakbalaskan dengan pelbagai nisbah Epoxidized Palm Olein (EPOo) dan Refined Bleached Deodorized Palm Kernel Olein (RBDPKOo). Poliol ini kemudiannya ditindakbalaskan dengan diisosianat dan dengan kehadiran katalis AlCl3-THF untuk menghasilkan poliuretana keras. Dua jenis hasil sampingan, iaitu “oxazolidone” dan isosianurat telah dihasilkan dan telah memperbaiki mutu busa keras. Ini adalah kerana dietanolamida yang mempunyai kumpulan epoksi telah menghasilkan poliuretana keras yang lebih bermutu dari segi mekanik dan kestabilan haba. Busa tersebut adalah stabil apabila disimpan pada suhu 70 °C dan -25 °C. Analisa termagravimetrik (TGA) menunjukkan bahawa suhu penguraiaan busa adalah lebih tinggi apabila dietanolamida yang mengandungi epoksi yang lebih tinggi digunakan dalam tindakbalas penghasilan busa. Indeks isosianat 1.40 telah dipilih sebagai indeks optima disebabkan penghasilan busa yang tidak rapuh serta berkekonduksian haba(0.0288 w/m.K) yang lebih rendah, berkekuatan ketegangan (338.8 kPa) dan berkandungan sel tertutup (97.95%) yang tertinggi. Poliester poliol juga disintesiskan dengan pembukaan kumpulan epoksi dari EPOo dengan asid dikarboksilik yang berantai C6 ke C12. Poliester poliol ini dicampur separuh dengan poliol polieter komersial dan seterusnya ditindakbalaskan dengan toluena diisosianat dalam penyediaan busa fleksibel. Asid dikarboksilik yang berantai lebih panjang didapati adalah lebih reaktif dengan menghasilkan poliol yang bernilai hidroksi yang lebih tinggi (103.6 mg KOH/g sample). Busa yang dihasilkan juga mempunyai nilai “hysteresis” yang lebih rendah, nilai pemanjangan sehingga putus yang lebih tinggi serta kestabilan haba yang lebih baik. Suhu penguraian yang dikaji dengan analisa TGA dan “Differential Scanning Calorimeter” (DSC) bagi busa yang dihasilkan oleh poliester poliol berantai panjang didapati adalah lebih tinggi. Akan tetapi, busa yang dihasilkan oleh poliol berantai pendek mempunyai nilai kekuatan ketegangan dan ketahanan dikoyak yang lebih tinggi. Indeks isosianat 1.00 dan kandungan air 2 g yang digunakan sebagai agen peniup dalam formula penghasilan busa fleksibel telah dipilih sebagai indeks dan kandungan air yang optima. Mikroskop optik menunjukkan sel-sel terbuka dalam busa adalah berbentuk pentagon dan mempunyai saiz-saiz yang tidak seragam bergantung kepada kandungan air yang digunakan semasa penghasilan busa. <br/> <br/>Description: Thesis (PhD) -- Faculty of Science, University of Malaya, 2008. Tue, 01 Jan 2008 00:00:00 GMT http://dspace.fsktm.um.edu.my/handle/1812/602 Title: System analysis and design of Musaceae genetic resources knowledge base <br/> <br/>Authors: Rohana Che Nordin <br/> <br/>Abstract: System Analysis and Design of Musaceae Genetic Resources Knowledgebase was about a unique database of data mining with a combination of Imaging and Checklist Database and Genetic Resources itself and was first develop in Malaysia and also over the world. Application ‘Checklist Decision Support’ helps to identify the species of Musaceae (according to ‘Flora of Malaya by Hottum). Imaging database storing the specimen voucher digitally was also the first developed system. This database can support the common software that had been used by taxonomist like BRAHMS and DELTA. This integration data has been name as “BANANA (Musaceae) GENETIC RESOURCES DATABASE SYSTEM (BGRDS)”. The methodology of this project contains using the software of Case Studio 2.16 and FileMaker pro 7.Besides it includes the image capturing and storage in the data under ‘Data Capture, Clean Up and Interpretation’. This database hopefully gives a lot of advantages to researchers and students by its contents and design. This database was designed to become the first developed system which has a unique database and useful potential to taxonomist, genetic conservations, scientist and public. <br/> <br/>Description: Dissertation -- Faculty of Science, University of Malaya, 2004. Thu, 01 Jan 2004 00:00:00 GMT http://dspace.fsktm.um.edu.my/handle/1812/600 Title: The population biology of straits Rhododendron (Melastoma malabathricum L.) <br/> <br/>Authors: Faravani, Mahdi <br/> <br/>Abstract: Straits Rhododenron (Melastoma malabathricum L. )(Melastomataceae) is a weedy invasive and medicinal shrub in arable lands, abandoned farmlands, secondary forest openings and derelict areas in Malaysia. Experiments were conducted to determine the effects of chemical media, light and temperature regimes on seed germination and clonal growth of M. malabathricum. Branching pattern, inter-plant spacing, selfthinning, allelopathy and antioxidant activity of M. malabathricum were also investigated in this study. Seeds of M. malabathricum were collected from the campus of the University of Malaya, Kuala Lumpur (3o 8’ N; 101o 42’ E), Malaysia. Moderate germination percentages ranging from 37% to 40% were recorded at 25-30 oC for oven-dried seeds. Seed germination was positively photoblastic. No seed germination prevailed in darkness, or when exposed to chemical media, and at temperature regimes < 20 oC. Light regime strongly influenced clonal growth of M. malabathricum. Mathematical models were developed for M. malabathricum describing branching networks, directionality and dispersion of branches with respect to the mother plant as influenced by density. The aim of this study was to determine if uniform branch patterns existed or changed in relation to density or plant height. Circular statistics were applied to test whether a plant with close neighbours responded either by investing in branch growth away from the competitive pressure or simply into zones free of neighbours. Rayleigh’s uniformity tests showed that the horizontal rotation angle φ was uniformly distributed and, but the distributions of the vertical rotation angle Ө was uni-modal form. The Ө angles were distributed in plants at different densities registering respective mean direction of 52.3°, 47.8° and 41.8° from the lowest to the highest density, respectively. The effect of inter-plant spacing on the growth of individual plants in an increased space and with equal sample size (number of plants) for each spacing gradient was investigated under varying plant spacing (2, 3, 7, 13, 25, 50 and 98 plants/m-2). The experimental design consisted of plants positioned in a polar coordinate grid with seven arcs, eighteen rays and an angle of 20o. The distance between arcs increased exponentially from 6 cm to 43 cm. Rays were separated by an angle of 20o. Straits Rhododenron showed very high survival percentages even when planted in high densities for a period of 200-odd days after planting. Widely-spaced plants were significantly taller than the more closely spaced plants of the same cohort. Mean stem diameter, plant biomass, number of leaves and branches, and branch length increased with increase in plant (wider) spacing. The results support the concept of competition in the self-thinning rule. Intra-specific competition had a profound effect on the number of individuals in a population, as illustrated by the log of average leaf weight per plant plotted against the log of density of survivors for a plant population. The leaf population's trajectory was held under a line of slope -1.12 (R2 = 0.58, p<0.05). The antioxidant activities of crude extracts of M. malabathricum in the laboratory were also been assessed. The effects of methanol extracts of both root and shoot were investigated for their radical scavenging activity using DPPH assay. The methanol extracts were able to reduce the stable free-radical DPPH to the yellow – colored diphenylpicrylhydrazine with an IC50 of 141.88μg/ml and 154.48μg/ml for leaf and root methanol extracts, respectively, but these were measurably lower than ascorbic acid at 28.61 μg/ml. In the study of allelopathy, aqueous extracts were assayed from fresh materials with concentrations of 0, 50, 100, 150 and 200gL-1. The parallel concentrations of aqueous extracts of oven-dried materials used were 40, 80, 120, 160, and 200 gL-1. Inhibition of seed germination of radish prevailed at concentrations above 200gL-1 of the aqueous extract of dried materials, while with methanol extract similar inhibitions were observed at concentrations ranged of 14.28 - 30 gL-1. Total inhibition of root and shoot growths was also observed in barnyardgrass. Both species were susceptible to allelochemical extracts isolated from shoot and root of M. malabathricum. Root and shoot lengths of radish and barnyardgrass decreased with the application of the extracts. The results were discussed from the viewpoint of using the extracts as a natural herbicide to control barnyardgrass and other susceptible weed species by arresting seed germination, seedling growth and establishment. The results of studies embodied in this thesis may provide insights on the processes involved in the population regulation of M. malabathricum. Arguably, these processes precisely are involved leading to colonization and consequential establishment of open spaces by invasive plant species. <br/> <br/>Description: Thesis (PhD) -- Faculty of Science, University of Malaya, 2008. Sat, 01 Nov 2008 00:00:00 GMT http://dspace.fsktm.um.edu.my/handle/1812/599 Title: PECVD hydrogenated amorphous carbon films: Growth and characterization <br/> <br/>Authors: Rozidawati Awang <br/> <br/>Abstract: This research offers critical insights on the growth and characterization of hydrogenated amorphous carbon (a-C:H) thin films by plasma enhanced chemical vapour deposition (PECVD). The initial phase of this work involved designing and building the reaction chamber for the PECVD system intended for the preparation of a-C:H thin films. The second phase is focused on ensuring that the PECVD system is capable of producing good quality and reproducible a-C:H films. The effects of RF discharge power on the optical and chemical bonding properties of the films are investigated. These results are used to explain the deposition kinetics of the films and to check for consistencies with published results. The third phase was focused on studying the effects of deposition time and film thickness on the optical and chemical bonding properties of the films prepared at high and low RF powers. The study on the influence of hydrogen (H2) and helium (He) dilution of methane (CH4) on the optical and chemical bonding properties of the films deposited by direct current (DC) PECVD is the focus of the fourth phase of this work. The final phase investigates the effects of deposition time and film thickness on the optical and chemical bonding properties of the films deposited by DC PECVD using H2 or He diluted CH4. These films are deposited using high and low H2/He to CH4 flow-rate ratios. Optical transmission spectroscopy, Fourier transform infrared (FTIR)spectroscopy and micro-Raman scattering spectroscopy are used to study the optical and chemical bonding properties of the films. The results of this work demonstrated that increase in RF discharge power increased the deposition rate and the sp2 fraction in the films but significantly reduced the optical band gap, Eg, H content and sp2 cluster size. These results were consistent with published results and the variation of the properties of the films with RF power was consistent with the deposition kinetics of the a-C:H films. This confirmed that the home-built PECVD system designed and built for this work was capable of producing good quality and reproducible a-C:H films. Eg and sp2 cluster size were found to be dependent on deposition time and film thickness. These parameters decreased with increase in film thickness. An increase in deposition time resulted with an increase in sp2 fraction and disorder in the film structure. The sp2 C content increased and H content in the films decreased with increase in diluent gas (H or He) to CH4 flow-rate ratio. Long deposition time retarded the growth rate of a-C:H films due to etching effects in films deposited from both H2 and He diluted methane. Increase in deposition time increased the sp2 C content in the film structure which consistently led to a decrease in Eg. In H2 diluted methane films, long deposition times allowed longer exposure to the H etching effect resulting in the creation of small sp2 clusters which reduced bond angle distortion and increased the distribution of cluster sizes. In helium diluted methane films, longer exposure to hydrocarbon ion bombardment has comparatively very small effects on the size and structural disorder in the films. ABSTRAK Penyelidikan ini mendalami kaedah pemendapan dan pencirian filem nipis amorfus karbon berhidrogen (a-C:H) daripada teknik pemendapan wap kimia secara peningkatan plasma (PWKPP). Fasa pertama penyelidikan ini adalah merekabentuk ruang tindakbalas dan membina sistem PWKPP untuk menghasilkan sampel-sampel filem a-C:H. Fasa kedua memfokus kepada penentuan keupayaan sistem PWKPP berfungsi untuk menghasilkan filem a-C:H berkualiti tinggi serta keboleh-ulangan penyediaan sampel. Kesan kuasa frekuensi radio (FR) kepada sifat optik dan ikatan kimia filem dikaji. Hasilnya digunakan untuk menerangkan kinetik pemendapan filem dan menyemak kesetaraan hasil yang diperolehi oleh penyelidik-penyelidik lain. Fasa ketiga memfokus kepada kesan masa pemendapan dan ketebalan filem terhadap sifat optik dan ikatan kimia filem yang dihasilkan pada keadaan FR kuasa tinggi dan rendah. Kajian ke atas kesan gas metana (CH4) yang dicampurkan dengan gas hydrogen (H2) atau gas helium (He) kepada sifat optik dan ikatan kimia filem yang dimendapkan daripada PWKPP arus terus (AT) merupakan fokus kajian fasa keempat. Fasa terakhir mengkaji kesan masa pemendapan dan ketebalan filem terhadap sifat optik dan ikatan kimia filem yang dihasilkan oleh PWKPP AT menggunakan gas metana yang dicampurkan dengan gas hidrogen atau gas helium. Filem-filem ini dimendap menggunakan nisbah kadar-aliran H2/ He kepada CH4 pada keadaan nisbah tinggi dan rendah. Spektroskopi pemancar optik (UV-Nir-Vis), spektroskopi Transformasi Fourier Inframerah (FTIR) dan spektroskopi-mikro Raman digunakan untuk pencirian sifat optik dan ikatan kimia filem. Hasil penyelidikan ini menunjukkan peningkatan kuasa FR meningkatkan kadar pemendapan dan kandungan sp2 di dalam filem tetapi menurunkan nilai Eg,kandungan H dan saiz kluster sp2. Hasil ini setara dengan hasil yang telah diterbitkan dan variasi sifat filem dengan kuasa FR adalah setara dengan kinetik pemendapan filem a-C:H. Maka, dapat disahkan bahawa sistem PWKPP yang dibina ini berfungsi dengan baik, menghasilkan filem a-C:H berkualiti tinggi dan penyediaannya bolehulang. Nilai Eg dan saiz kluster sp2 di dapati bergantung kepada masa pemendapan dan ketebalan filem. Parameter ini berkurang apabila ketebalan filem bertambah. Peningkatan masa pemendapan meningkatkan kandungan sp2 dan ketidaktertiban struktur filem. Kandungan sp2 bertambah dan kandungan H berkurang bila nisbah kadar-aliran gas campuran (H2 atau He) terhadap gas CH4 ditingkatkan. Peningkatan masa pemendapan merencatkan kadar pemendapan filem a-C:H disebabkan kesan pemunaran di dalam filem yang dimendapkan daripada kedua-dua keadaan H2 atau. He dicampurkan dengan gas CH4. Peningkatan masa pemendapan meningkatan kandungan sp2 di dalam struktur filem yang menyebabkan penurunan nilai Eg. Bagi filem daripada CH4 yang dicampurkan dengan H2, pemanjangan masa pemendapan membenarkan lebih pendedahan kepada proses pemunaran yang menyebabkan penghasilan kluster sp2 bersaiz kecil yang mengurangkan herotan sudut ikatan dan meningkatkan taburan saiz kluster. Bagi filem daripada CH4 yang dicampurkan dengan He, pemanjangan masa pendedahan kepada proses pemunaran oleh ion hidrokarbon berkelajuan tinggi di dapati hanya memberi kesan yang kecil terhadap saiz kluster dan ketidaktertiban struktur filem. <br/> <br/>Description: Thesis (PhD) -- Faculty of Science, University of Malaya, 2008. Tue, 01 Jul 2008 00:00:00 GMT http://dspace.fsktm.um.edu.my/handle/1812/597 Title: Application of Eichhornia crassipes (water hyacinth) and Pistia stratiotes (water lettuce) as tertiary wastewater treatment agents <br/> <br/>Authors: Siti Zulaikha Othman <br/> <br/>Abstract: ABSTRACT Eichhornia crassipes (Mart.) Solms (water hyacinth) and Pistia stratiotes L. (water lettuce) were studied to gauge the effectiveness of nutrients, bacteria and heavy metals removal in domestic and small-scale industry sewage of Kuala Lumpur city. Both were grown in approximately 68 L wastewater with 21-days retention period in fiberglass tanks. Readings for water temperature, turbidity, specific conductance, pH, dissolved oxygen (DO), chlorophyll a, ammonium-nitrogen (NH4-N) and nitrate-nitrogen (NO3-N) were taken in-situ every five days, whilst analysis for total suspended solid (TSS), biochemical oxygen demand (BOD5), chemical oxygen demand (COD), alkalinity, nitrite-nitrogen (NO2-N), orthophosphate (PO4-P), enumeration of total bacteria, heavy metals (Cd, Cu, Zn) content were done in the laboratory. Water temperature with plants was in the range of 24.9oC to 27.5oC; whilst the mean for pH in the E. crassipes and P. stratiotes microcosms were 7.3 and 7.7 respectively. The removal efficiency by both plants was in the range of 50 to 93% for BOD5, 9 to 75% for COD, and 6 to 100% for TSS. An increase in the concentration of dissolved oxygen from 4 to 52% was also observed although in some cases there was a decrease in the concentration of DO. There were drastic drops in not only NH4-N but also NO3-N content in the water. The range of decrease of NH4-N was from 30 to 96% in both tanks. However, untreated water had a higher removal efficiency of NH4-N (99%) compared to the treated water due to the consumption by the algae which has been observed had grew in the tanks. In contrast, NO3-N content in the water was found to have been removed greatly by both plants from 0.2 to 12.7 mgL-1 and PO4-P content from 1.51 to 6 mgL-1 compared to the untreated water which was from 14 to 28.2 mgL-1 (NO3-N) and from 5.3 to 11.1 mgL-1 (PO4-P). Enumerations of total bacteria decreased from 30 to 81%, although the number of colonies formed sometimes were higher with root’s plants presence. As well as chlorophyll a or algae concentration which the growth were inhibited by the macrophytes and decreased from 20 to 52% compared to the control. The heavy metal concentrations in the sewage also dropped (Cd, 94.7%; Cu, 92%; Zn, 95.2%) as they were efficiently absorbed by both macrophytes especially by their roots, leaves and followed by stems (E. crassipes). In overall, the sewage effluent quality was much improved after undergo the treatment. ABSTRAK Kajian terhadap Eichhornia crassipes (Mart.) Solms (keladi bunting) dan Pistia stratiotes L. (kiambang) telah dijalankan bagi menguji tahap keefisienan untuk mengurangkan kandungan nutrien, bakteria dan logam berat dalam air kumbahan domestik dan industri kecil-kecilan di Kuala Lumpur. Tumbuhan diletakkan di dalam tangki yang berisi kira-kira 68 L air kumbahan selama 21 hari. Bacaan suhu air, kekeruhan, konduktiviti, pH, oksigen terlarut, klorofil a, nitrogen-ammonium (NH4-N) dan nitrogen-nitrat (NO3-N) diambil secara in-situ setiap lima hari, manakala analisis untuk jumlah pepejal terampai (TSS), keperluan oksigen biokimia (BOD5), keperluan oksigen kimia (COD), alkaliniti, nitrogen-nitrit (NO2-N), ortofosfat (PO4-P), penjumlahan bakteria dan kepekatan logam berat (Cd, Cu, Zn) dilakukan di dalam makmal. Suhu air yang mengandungi tumbuhan adalah dalam julat 24.9 oC hingga 27.5oC; manakala purata untuk pH air tangki E. crassipes and P. stratiotes adalah masing-masing 7.3 and 7.7. Keefisenan kedua-dua tumbuhan dalam pengurangan BOD5 adalah 50 hingga 93%, 9 hingga 75% (COD), dan 6 hingga 100% (TSS). Peningkatan oksigen terlarut dari 4 to 52% turut diperhatikan walaupun terdapat beberapa penurunan. Terdapat penurunan yang ketara bagi kandungan NH4-N (30 hingga 96%) dan NO3-N dalam air kedua-dua tangki tumbuhan. Bagaimanapun, air kumbahan yang tidak dirawat mempunyai kadar pengurangan yang lebih tinggi berbanding air yang dirawat akibat penggunaannya oleh alga. Sebaliknya, kandungan NO3-N dalam air yang dirawat oleh kedua-dua tumbuhan telah mengurang dengan banyak dari 0.2 hingga 12.7 mgL-1 dan kandungan PO4-P pula dari 1.51 hingga 6 mgL-1 berbanding air yang tidak dirawat iaitu dari14 hingga 28.2 mgL-1 (NO3-N) dan dari 5.3 hingga 11.1 mgL-1 (PO4-P). Penjumlahan bakteria telah mengurang sebanyak 30 hingga 81%, walaupun adakalanya bilangan koloni yang terbentuk lebih tinggi dengan kehadiran akar tumbuhan. Begitu juga dengan jumlah klorofil a yang pertumbuhannya dihalang oleh tumbuhan akuatik sebanyak 20 hingga 52% berbanding kawalan. Kandungan logam berat di dalam air kumbahan juga menurun (Cd, 94.7%; Cu, 92%; Zn, 95.2%) kerana keefisienan penyerapan oleh kedua-dua tumbuhan terutamanya oleh bahagian akar, daun dan diikuti oleh bahagian batang (E. crassipes). Kesimpulannya, kualiti air kumbahan yang dihasilkan adalah lebih baik selepas melalui rawatan. <br/> <br/>Description: Dissertation -- Faculty of Science, University of Malaya, 2009. Wed, 01 Oct 2008 00:00:00 GMT http://dspace.fsktm.um.edu.my/handle/1812/592 Title: Electrophoretic studies of surface charge on unicellular bacteria <br/> <br/>Authors: Lee, Poh Foong <br/> <br/>Abstract: Electrophoretic studies of surface charge on unicellular cell were carried out. The unicellular bacteria selected for this research consisted of two different strains, which are gram-positive S.aureus and gram-negative E.coli. Colloidal particles, (Titanium dioxide) TiO2, and liposome, were used as non-living counterparts for comparison. The studies have focused on the effects of different physical and chemical conditions, including variations of temperatures, applied field, and time intervals between measurements. We did calculations of the Donnan potential and also investigated the polarizability of the bacteria. Methodology used in this research was laser Doppler velocimetry electrophoresis. Surface charge of bacteria cells is measured with electrophoresis due to development of net charge at the particle surface affects the distribution of ions in the surrounding interfacial region. This process increases concentration of counterions (ions of opposite charge to that of the particle) close to the surface. Zeta potential is considered to be the electric potential of this inner area including this conceptual "sliding surface". The electrophoretic mobility ( μ ) is the migration rate of the charged particles to the electrode when electric field is applied. In various pH, dead cells of both E.coli and S.aureus exhibited lower electrophoretic mobility than live cells. This was mainly due to dead cell had lost the metabolic activity to give charge balance to surface charges. Besides, it was found that increase in the ionic strengths of NH4Cl in the buffer reduced the electrophoretic mobility of samples. In contrary, increased ionic strengths of NaCl obtained the opposite result for the bacteria. This might be due to the increase of influx Na+ into cells, which increases the anionic lipid to balance the charges in the cells. Results indicated that both approaches fitted well at greater ionic strength of NaCl with the Donnan potential approximation. The electrophoretic mobility of live E.coli displayed a mild increase at higher temperatures. On the other hand, results indicated only a slight increase in negative electrophoretic mobility of live S.aureus as the temperature increased. Increase in applied field increased the electrophoretic mobility of bacteria and colloidal particles due to the stronger attraction field. Different time intervals between measurements with unchanged conditions showed that higher zeta potential was measured for time intervals more than 10s between measurements. This indicated that the particles still swirled around when the next measurements started. In addition, live bacteria recorded greater polarizability compare to colloidal particles. This may be attributed to the semipermeable cell membrane of live cells which hasten the ions exchange between the cell interior and the external environment. A greater polarization of E.coli was obtained, which possessed thinner cell wall peptidoglycan layer compared to S.aureus. The conductivity and permittivity of cells increased as the frequency increased. However, the permittivity of cells were shown constant at higher frequency (>200Hz). <br/> <br/>Description: Thesis (PhD) -- Faculty of Science, University of Malaya, 2009. Wed, 01 Apr 2009 00:00:00 GMT