A Study of the Effects of Solution and Process Parameters on the Electrospinning Process and Nanofibre Morphology

Nanofibres have been the subject of recent intensive research due to their unique properties, especially their large surface-area-to-volume ratio, which is about one thousand times higher than that of a human hair. They also have several other remarkable characteristics, such as flexibility in surface functionality, superior mechanical properties such as stiffness and tensile strength, their capacity to be formed into a variety of shapes, and the fact that they can be produced from a wide range of organic and inorganic polymers. These outstanding properties make polymer nanofibres the optimal candidates for providing significant improvement in current technology and for opening the door to novel applications in many research areas. Electrospinning is a straightforward and inexpensive process that produces continuous nanofibres from submicron diameters down to nanometre diameters. Many researchers have successfully electrospun a variety of polymer solutions into nanofibres. However, electrospinning any polymer solution directly is not straightforward or simple because of the number of parameters that influence the electrospinning process. The characteristics of the electrospun jet and the morphology of the resultant fibres are highly dependent on the properties of the polymer solution. In addition, what are favourable processing conditions for one polymer solution may not be suitable for another solution. A literature review revealed that there is no clear understanding of the behaviour of the electrospun jet and the way in which fibre morphology varies with variations in influential parameters. In addition, reported results contain significant inconsistencies and very little research has examined the effects of electrical parameters such as the electric field, the polarity of the electrode, and the conductivity and permittivity of the solution. Furthermore, no research has been conducted with respect to optimizing the electrospinning process. In this thesis, a comprehensive study was carried out by giving a special attention to the effects of electric field that have not been thoroughly investigated in the past. The electric field between the needle tip and the collector plate was altered by varying the applied voltage, distance between the needle tip and the collector plate, the inner diameter of the needle, and polarity of the voltage. Based on the experimental work, it was found that the behavior of Taylor cone, the length of the straight jet portion, and whipping jet region is highly influenced by the distribution of the electric field between the needle tip and the collector plate. Based on the stability of the Taylor cone, it was concluded that the stable operating region of the electrospun jet is a very narrow region and it is between 0.9 – 1.1kV/mm for the range of experiments that were carried out in this study. The length of the straight jet portion of the electrospun jet shows a linear relationship to the applied electric field at the tip of the fluid droplet and the whipping jet region is influenced by both the electric field at the tip of the fluid droplet and the distance between the needle and the collector plate. A confirmation were made that there must be enough distance between the needle tip and the collector plate (>200mm) to operate over the complete range of voltages without affecting drying of nanofibres. It was also concluded that the morphology and diameter of the collected nanofibres depend significantly on both the length of the straight jet portion and size of the whipping region. The effects of polarity of the applied voltage on the electrospinning process and nanofibre morphology were investigated using the positive, negative, and AC voltages. However, it was found that the electrospinning can not be achieved with the application of 60Hz AC voltage. It was observed that the behavior of Taylor cone, the straight jet portion, and the whipping jet region depend on the polarity of the applied voltage. During the study, it was accomplished that the reason for this different behavior is the disparity of ionization in the polymer solution with the application of positive and negative high voltages. In this thesis, the effects of multi-needle arrangements on the electrospinning process and fibre morphology were also explained. Finite element method (FEM) simulation results revealed that the local electric field strength around each needle tip weakens significantly in the case of multi-needle schemes due to the mutual influence of other needles in the arrangement compared to the single-needle system. The spacing between the needles was varied, and the effects of the needle spacing were examined. The experimental and simulation results were concealed the correlation between the degree of field distortion and the variation in the measured vertical angle of the straight jet portion for different needle spacing. It was concluded that the local field deterioration at the needle tips in multi-needle schemes degrades the electrospinning process significantly and produces considerable variation in the fibre morphology even though the influence of needle spacing on the average jet current and the fibre diameter are not very significant. In this work, the effects of conductivity and ionic carriers on the process of electrospinning and hence on the morphology of nanofibres were studied using polyethylene oxide (PEO) and polyacrylic acid (PAA) aqueous solutions. Different salts including lithium chloride (LiCl), sodium chloride (NaCl), sodium fluoride (NaF), sodium bicarbonate (NaHCO3), potassium chloride (KCl), and cesium chloride (CsCl) were added in different concentrations to the polymer solutions for introducing different ionic carriers into the solution. The results showed that the average fiber diameter decreases with increase in the conductivity of the solution. In addition, it was discovered that the formation of Taylor cone highly depends on the conductivity in the polymer solution. Formation of multi-jets at the fluid droplet when the conductivity of the polymer solution is increased during the electrospinning was also observed. These behaviors were completely explained using the distribution of the surface charge around the electrospun jet and the variation in the tangential electric field along the surface of the fluid droplet. The stretching of the polymer jet can be related to the amount of ionic carries and the size and mobility of positive and negative ions. The increasing amount of ionic carriers and smaller size positive ions enhance the stretching of the electrospun jet. In contrast, the lesser diameter negative ions decrease the stretching of the electrospun jet. The morphology of electrospun nanofibres can also be varied by altering the type of ionic carriers. A charge modifier, which is a container that is used to hold a solvent surrounding the needle tip during the electrospinning, was introduced to facilitate the electrospinning of insulating and high conductivity polymer solutions. The co-axial flow of the filled solvent on the outer surface of the polymer solution helps to induce enough surface charges during electrospinning and it also keeps the electric field tangential to the fluid surface during the process. Therefore, the introduction of charge modifier greatly enhanced the electrospinning behavior of highly insulating and conductive polymer solutions and liquids. The developed charge modifier method was verified by using sodium alginate which is a biopolymer that cannot electrospin alone due to its high electrical conductivity and silicone rubber which is an insulating liquid polymer at room temperature. One of the most commonly used theoretical model of the electrospinning process was modified to incorporate the non-uniform characteristics of the electric field at the tip of the needle. The non-uniform electric field between the needle tip (spinneret) and the collector plate was calculated based on the charge simulation technique (CST). It gives a better representation of the true electrospinning environment compared to the uniform field calculation in the existing model. In addition, a localized approximation was used to calculate the bending electric force acting on the electrospinning jet segments. It was also introduced a constant velocity to initiate the electrospinning jet during simulation. The incorporated modifications gave better results that closely match with the real electrospinning jet. The modified electrospinning model was used to understand the effects of parameters on the electrospinning process and fibre morphology

フクシマダイイチゲンシリョクハツデンショジコゴニオケルタケオヨビモクザイノコンポストリヨウニカンスルケンキュウ

博士（農学)東京農工大

Assessment of Irrigation Scheduling in Pelwatte Seed Cane Plantation

Sugarcane (Saccharum officinarum L) is mainly grown in the dry zone of Sri Lanka wherethe major soil group is well drained Reddish Brown Earth. Pelwatte Sugar Industries Limitedcultivates more than 4,000 hectare of sugarcane. Uneven and unpredictable rainfall in the dryzone makes it necessary of the irrigation. This research project was conducted to develop analternative system to overcome weaknesses of the existing irrigation system. Irrigationinterval, irrigation time and net irrigation depth was measured via a number of equations,which used in irrigation scheduling. Distribution uniformity was found by three can tests forexisting and suggested spacing and those tests were helpful to find irrigation rate. Othermiscellaneous practices are equal for both suggested and existing systems. Irrigation intervalof the existing system is around 10 to 14 days. Irrigation time is 3 hours. Irrigation rate of thesystem is 6.30 mm hr-1. Net irrigation depth is 18.7 mm; hence water requirement per hectareis 186.75 m3. Spacing used in existing sprinkler system is 18 m × 18 m and averagedistribution uniformity is 55.71%. Area covered in a day is 1.7 hectare. Fuel cost per hectareis Rs. 3,395.00. Suggested irrigation interval of the study was 14 days. Net irrigation depthwas 33.2 mm. Two spacing systems were suggested, 18 m × 12 m spacing system and 12 m ×12m system. Distribution uniformity and discharge rate increment of the two systems wasstatistically significant over existing system. Their values and corresponding p values are70.8%, 0.026 and 10.427 mm hr-1, 0.002 for 18 m × 12 m system and 83.5%, 0.007 and 16.6mm hr-1, 0.014 for 12 m × 12m system respectively. Irrigation time, area covered within aday, water requirement per hectare and fuel cost per hectare for 18 m × 12 m system areconsecutively 3 hours and 11 minutes, 1.2 hectare, 332.49 m3 and Rs. 6,034.00 and for 12 m× 12 m system are 2 hours, 1.1 hectare, 332.49 m3 and Rs. 5,060.00. It can be concluded thatboth suggested systems were improved distribution uniformity and irrigation ratesignificantly. Moreover, net irrigation depth of the new system was almost twice compared toexisting system, which explains the inadequate wetting of the existing system. 12 m × 12 msystem is superior over both 18 m × 12 m spacing and existing system

Comparative assessment of intensive tomato production in innovative non-circulating aquaponics vs. conventional hydroponics

New tendencies in farming techniques which include a composite agricultural production system have evolved as solutions for uninterrupted food supply. Production of high-yielding good-quality tomato (Solanum lycopersicum L.) is one of the leading challenges. This study aimed at evaluating the growth, yield, and fruit quality of hybrid tomato (Umagna), cultivated in non-circulating aquaponics and conventional hydroponics systems. A unique and innovative non-recirculating deep water culture aquaponics system (DWCAS) was developed as a prerequisite for high productivity comparable to current stand-alone fish/plant facilities. Including DWCAS, two other conventional hydroponics systems were compared during the study; the deep water culture hydroponics system (DWCHS) and the open bag system (OBS). The assessment of the production systems was based on the growth behavior, tomato yield, and quality. The maximum yield was observed for the DWCHS followed by DWCAS. The least yield was observed for the OBS. The results demonstrated the highest average fruit weight and marketable yield produced by DWCHS. There was no difference in plant dry matter content among production systems. The fertilizer use efficiency was increased by 11.7% and 85.86% in favor of the DWCHS and DWCAS, respectively.  The total rainwater use efficiency was also increased in DWCHS

Comparative study of thermal efficiency in five different fuel wood cook stoves for conserving biomass energy sources in Sri Lanka

Minimum energy requirements for cooking and heating may be estimated as 6 - 10 GJ, or 0.5 - 1 m³ of fuel wood per person per year. Inefficient use of biomass for anthropogenic activities causes reduction of biomass availability. Therefore, there is a scientific need to identify most efficient cook stoves to improve the efficiency of using bio mass for cooking for the sake of saving forest cover and for the solution of the green energy requirement.The present research study formulated to evaluate the efficiency of existing cook stoves such as “Batapola Lipa” (BS), “Anagi Lipa” (AS), and traditional three stone cook stove (TS) with newly developed cook stoves such as traditional three stone cook stove with grater (TSG) and a prototype metal stove (PMS) developed by the Department of Agricultural Engineering, Faculty of Agriculture, University of Ruhuna. The standard boiling water laboratory test was done for studying the thermal efficiency. Cinnamon sticks were used as the source of biomass. Initial and boiling water temperatures, amount of water boiled and evaporated, amount of biomass utilized and unburned remaining biomass in weight basis after the boiling test, were measured and percent heat utilized and power output of stoves were calculated.The results which were analyzed using ANOVA procedure with Duncan’s Multiple Range Test, revealed that energy output of the BS, AS, TS, TSG and PMS, were observed as 15.1 kW, 5.8 kW, 3.9 kW, 4.7 kW and 14.3 kW respectively. Comparatively higher percent heat utilized value were observed in TSG, AS and BS than TS and PMS. The BS, TS, TSG, PMS consumed 190, 274, 172, 298 g, within 3.95, 22, 11.25, 6.52 minutes respectively. Lowest biomass consumption rate was observed in TSG. It revealed that 102 g of biomass and 10.75 minutes can be saved by TSG than TS for boiling one liter of water. Therefore the significant amount of fuel wood can be saved successfully by introducing a grater to the traditional three stone cook stove which may save natural forests resources in Sri Lanka

Spatiotemporal analysis of fMR images

This thesis investigates the spatiotemporal analysis of functional MR images. Presently, most existing techniques fot the analysis of functional images are conducted in spatial and temporal domains separately. This projects investigates a model based approach to carry out the spatiotemporal analysis simultaneously in both spatial and temporal domains.Master of Engineering (SCE

Fine Needle Elastography (FNE) for biomechanically determining needle insertion forces and quantitative assessment of intranodular heterogeneity in tissue mechanical properties

Diseased tissues exhibit changes in mechanical properties and thus possess clinical diagnostic significance. This dissertation focuses mainly on thyroid nodules that are commonly found in about 19-67% of the population and 5-10% of which are carcinoma. Currently the primary method of thyroid nodule diagnosis - Fine Needle Aspiration Cytology (FNAC). FNAC has much room for improvement of diagnostic accuracy due to 15-32% nondiagnostic results and 20-30% indeterminate (suspicious) reports that lead for many complications for the patients. Furthermore, there is a wealth of variation of mechanical properties unique to different kinds of thyroid malignancies that are inaccessible with other existing methodologies. This dissertation introduces the novel concept of Fine Needle Elastography (FNE) and presents the design and development of a FNE Device prototype integrated with a FNAC needle that allows for quantitative and sensitive assessment of tissues and materials based on local variations in elastic, friction, and cutting forces on needle insertion. A piezoelectric force-sensor at the base of FNA needle measures the forces opposing needle penetration with the micrometer-scale resolution. The axial resolution (~20μm) of FNE device was tested using control mm size gelatin matrices and unripe pear in assessing needle penetration resistance, force heterogeneity and optimization of needle penetration velocity. Further, it is demonstrated the usefulness of FNE in quantitative, biomechanical differentiation of simulated thyroid tumor nodules in an ultrasound neck phantom. Fluid or solid nodules were probed in the phantom study coupled with real-time ultrasound guidance. The preliminary FNE data shows significantly higher force and stiffness variations (1-D Force Heterogeneity; HF,a=6.5mN, HF,q=8.25mN and Stiffness Heterogeneity; HS,a=0.0274kN/m, HS,q=0.0395kN/m) in solid nodules compared either to fluid nodules or to regions corresponding to simulated healthy thyroid tissue within the ultrasound phantom. Further investigation of the utility of the device in a proper clinical setting with excised thyroid tissue and in vivo testing of human subjects with different kinds of thyroid carcinoma can be used to develop a database of FNE data relating to each kind of thyroid nodule. The preliminary results suggest future applications of the FNE Device for in vivo FNE biopsies based on force and stiffness heterogeneity to diagnose thyroid nodules as an ancillary diagnostic tool in thyroid cancer management. FNE methodology could be potentially extended to diagnosis and management of other percutaneous diagnosis methodologies in diagnosing breast cancer, liver cancer etc

Automatic sleep stage classification using multitaper spectral estimation, wavelet transform and neural network

The full abstract for this thesis is available in the body of the thesis, and will be available when the embargo expires.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat

Bayesian Approach to Segmentation of Statistical Parametric Maps

A contextual segmentation technique to detect brain activation from functional brain images is presented in the Bayesian framework. Unlike earlier similar approaches [Holmes and Ford (1993) and Descombes et al. (1998)], a Markov random field (MRF) is used to represent configurations of activated brain voxels, and likelihoods given by statistical parametric maps (SPM's) are directly used to find the maximum a posteriori (MAP) estimation of segmentation. The iterative segmentation algorithm, which is based on a simulated annealing scheme, is fully data-driven and capable of analyzing experiments involving multiple-input stimuli. Simulation results and comparisons with the simple thresholding and the statistical parametric mapping (SPM) approaches are presented with synthetic images, and functional MR images acquired in memory retrieval and event-related working memory tasks. The experiments show that an MRF is a valid representation of the activation patterns obtained in functional brain images, and the present technique renders a superior segmentation scheme to the context-free approach and the SPM approach

Microwave exposure added characteristics to the wounding-induced variation potential of Aloe arborescens leaves

The influence of radiofrequency electromagnetic radiation on the wounding-induced electric potentials (EPs) in Aloe arborescens plants was investigated. Burn wounding-induced electrical potentials of mature A. arborescens plants were observed under the exposure of 2.45 ​GHz, 3.5 ​GHz and 5.5 ​GHz microwaves at incident power density 1.5 ​± ​0.2 ​W ​m−2. Aloe leaves were subjected to flame wounding at the leaf tips and propagation EPs were recorded by inserting a glass Ag/AgCl microelectrode into the leaf pulp. The propagation of electrical potential and a standard deviation of the fluctuations in electrical potential (SDEF) were investigated. The flame wounding generated propagating characteristic electric potential, and the exposure of microwaves added extra characteristics to the signals by reversing the electrical potential temporally for a shorter duration. The characteristics appeared in the repolarization phase of the signal under 2.45 ​GHz and 3.5 ​GHz exposure; for the 5.5 ​GHz exposure, 3 out of 6 characteristics appeared during the depolarization phase. Averaged polarization rates of the characteristics were increased with the increased microwave frequency. Added characteristics to the electric potential may have resulted from a secondary signal triggered due to microwave exposure, which should be further studied. The repolarization and depolarization rates of the wound signals were not different between control and microwave exposures. SDEFs were also not affected by microwave exposure