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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Organic Nanostructures and Devices using Electrostatic Processing

Sarkar, Soumayajit 01 January 2007 (has links)
Chemical sensors based on arrays of polymer-coated surface acoustic wave (SAW) devices are required for defense applications that provide a combination of sensitivity, selectivity, portability and response time. The primary challenge in the development of these polymer-based microsensors is the need to reproducibly deposit high quality, defect-free polymer coatings onto microelectrodes. Coating methods such as air brushing and solvent casting have proven unreliable and I have investigated the possibility of depositing polymer films on microelectrodes using electrostatic processing methods. In this work AC electrospraying was used to deposit nanoscale polymer films onto the surface of microelectrodes. The alternating polarity of the electric field eliminates surface charge accumulation and the polymers were deposited uniformly across both electrically insulating and conducting surface regions. In a different work, DC electrospraying was used to deposit patterned organic coatings onto the surface of microelectrodes. The surface of the microelectrode array consisted of an alternating pattern of insulating, grounded-metallic and ungrounded metallic regions, each with a width of 15µm. The charged particles were deposited only onto the grounded-metallic surface regions where there is an electrical path for charge dissipation. No polymer deposition was observed on the insulating or ungrounded-metallic regions due to the effects of surface charge accumulation. Also, I, DC electrodeposited organic molecules within the pores of ceramic film. Due to electrospraying, this film has a strong built-in electric field that induces Stark effect in the organic molecules, providing a unique new technology for bio and chemical sensing. Electrospinning has been used to produce polymer nanofibers with diameters ranging from a few microns to less than 100 nanometers. Due to mechanical oscillations of the electrically charged fibers during electrospinning, they are usually collected in the form of a non-woven mat without any significant fiber orientation. I have developed a new method for making highly aligned arrays of polymer nanofibers by using an AC coupled DC field to drive the electrospinning process. This new "biased AC electrospinning" method can be used to deposit aligned arrays of polymer nanofibers onto virtually any substrate. Potential applications of well-ordered nanofiber materials include tissue engineering, filtration, drug delivery and microelectronics.
12

On the use of cheap talk in hypothetical product valuation: a field experiment

Silva, Andres 15 May 2009 (has links)
Experimental willingness to pay (WTP) studies can be classified as hypothetical or non-hypothetical. In a hypothetical study, such as conjoint analysis, a subject does not need to make a real economic commitment. In contrast, in a non-hypothetical task such as in experimental auctions, a subject may need to actually buy the product. Subjects in hypothetical studies tend to overstate their true WTP. Consequently, researchers need to correct hypothetical values to obtain reliable WTP estimates. Recently, incentive-aligned and cheap talk approaches have been proposed as ways to correct for hypothetical bias. In a hypothetical task, a cheap talk script explicitly reminds the subject about the hypothetical nature of the task and its expected consequences. In an incentive-aligned task (non-hypothetical), subjects are randomly selected to physically buy the product. The objective of our study is to assess and compare the reduction of hypothetical bias in consumers’ willingness to pay for novel products by applying a generic, short, and neutral cheap talk script in a retail setting. To accomplish this objective, we employ non-hypothetical, hypothetical, and hypothetical with cheap talk treatments in our experimental design. We conducted our experimental retail study using conjoint analysis and open-ended elicitation mechanisms, utilizing Becker DeGroot Marshak (BDM) mechanism for the incentive-aligned treatments. Consistently in both elicitation mechanisms, using seemingly unrelated and random-effect Tobit techniques, we find that our cheap talk script is effective in eliminating the hypothetical bias. As expected, the hypothetical WTP values are significantly higher than the non-hypothetical values but the hypothetical values with cheap talk are not significantly different from incentive-aligned or non-hypothetical estimates. In addition, we find that open-ended estimates are significantly higher than conjoint analysis estimates and that emotions and familiarity can have significant impacts on WTP estimates.
13

Passively-aligned Optical Transceiver on Si Bench for Light Peak Application

Shiu, Jr-I 11 July 2011 (has links)
ABSTRACT The aim of this dissertation is to fabricate an optical transceiver based on Si-bench technology for light peak application. The transceivers are composed of hybrid integration of the vertical cavity surface-emitting lasers (VCSEL), photo diodes and multi-mode fibers (MMF) on the Si optical bench using V-groove and U-groove structures. We are able to passively align VCSEL to MMF and photo diode to MMF because of the accurately-aligned characteristic of V-groove. The 45-degree-angled fibers with mirror coating are used to bend the directions of both the incoming and outgoing lights to the photodiode and the MMF. The simulations showed that the optical losses of the transceiver are less than 10 dB when the distance between VCSEL and MMF is 250£gm.The measured optical losses between transmitting module and receiving module are less than 12 dB. Key words: Light Peak¡Boptical transceiver¡BSi-bench¡Baccurately-aligned
14

On the use of cheap talk in hypothetical product valuation: a field experiment

Silva, Andres 15 May 2009 (has links)
Experimental willingness to pay (WTP) studies can be classified as hypothetical or non-hypothetical. In a hypothetical study, such as conjoint analysis, a subject does not need to make a real economic commitment. In contrast, in a non-hypothetical task such as in experimental auctions, a subject may need to actually buy the product. Subjects in hypothetical studies tend to overstate their true WTP. Consequently, researchers need to correct hypothetical values to obtain reliable WTP estimates. Recently, incentive-aligned and cheap talk approaches have been proposed as ways to correct for hypothetical bias. In a hypothetical task, a cheap talk script explicitly reminds the subject about the hypothetical nature of the task and its expected consequences. In an incentive-aligned task (non-hypothetical), subjects are randomly selected to physically buy the product. The objective of our study is to assess and compare the reduction of hypothetical bias in consumers’ willingness to pay for novel products by applying a generic, short, and neutral cheap talk script in a retail setting. To accomplish this objective, we employ non-hypothetical, hypothetical, and hypothetical with cheap talk treatments in our experimental design. We conducted our experimental retail study using conjoint analysis and open-ended elicitation mechanisms, utilizing Becker DeGroot Marshak (BDM) mechanism for the incentive-aligned treatments. Consistently in both elicitation mechanisms, using seemingly unrelated and random-effect Tobit techniques, we find that our cheap talk script is effective in eliminating the hypothetical bias. As expected, the hypothetical WTP values are significantly higher than the non-hypothetical values but the hypothetical values with cheap talk are not significantly different from incentive-aligned or non-hypothetical estimates. In addition, we find that open-ended estimates are significantly higher than conjoint analysis estimates and that emotions and familiarity can have significant impacts on WTP estimates.
15

Vertically Aligned Nanocomposite Thin Films

Bi, Zhenxing 2011 May 1900 (has links)
Vertically aligned nanocomposite (VAN) thin films have recently stimulated significant research interest to achieve better material functionality or multifunctionalities. In VAN thin films, both phases grow epitaxially in parallel on given substrates and form a unique nano-checkerboard structure. Multiple strains, including the vertical strain which along the vertical interface and the substrate induced strain which along the film and substrate interface, exist in VAN thin films. The competition of these strains gives a promise to tune the material lattice structure and future more the nanocomposite film physical properties. Those two phases in the VAN thin films are selected based on their growth kinetics, thermodynamic stability and epitaxial growth ability on given substrates. In the present work, we investigated unique epitaxial two-phase VAN (BiFeO3)x:(Sm2O3)1-x and (La0.7Sr0.3MnO3)x:(Mn3O4)1-x thin film systems by pulsed laser deposition. These VAN thin films exhibit a highly ordered vertical columnar structure with good epitaxial quality. The strain of the two phases can be tuned by deposition parameters, e.g. deposition frequency and film composition. Their strain tunability is found to be related directly to the systematic variation of the column widths and domain structures. Their physical properties, such as dielectric loss and ferromagnetisms can be tuned systematically by this variation. The growth morphology, microstructure and material functionalities of VAN thin films can be varied by modifying the phase ratio, substrate orientation or deposition conditions. Systematic study has been done on growing (SrTiO3)0.5:(MgO)0.5 VAN thin films on SrTiO3 and MgO substrates, respectively. The variation of column width demonstrates the substrate induced strain plays another important role in the VAN thin film growth. The VAN thin films also hold promise in achieving porous thin films with ordered nanopores by thermal treatment. We selected (BiFeO3)0.5:(Sm2O3)0.5 VAN thin films as a template and get uniformly distributed bi-layered nanopores. Controllable porosity can be achieved by adjusting the microstructure of VAN (BiFeO3):(Sm2O3) thin films and the annealing parameters. In situ heating experiments within a transmission electron microscope column provide direct observations into the phases transformation, evaporation and structure reconstruction during the annealing. Systematic study in this dissertation demonstrate that the vertically aligned nanocomposite microstructure is a brand new architecture in thin films and an exciting approach that promises tunable material functionalities as well as novel nanostructures.
16

A new role for the non-aligned movement in a post-cold war era

Chetty, Mahesh January 2000 (has links)
With the disappearance of the superpower conflict that characterised the Cold War era, many observers have begun to question whether the Non-Aligned Movement (NAM) has a role to play in the post Cold War era. However the emergence of a number of issues on the international agenda, such as United Nations peacekeeping operations, global environmental issues and an increasing unwillingness on the part of the major economic powers to abide by GATT/WTO rules, have increasingly become of concern to non-aligned states. However whilst the United States has recognised that these issues require leadership in dealing with them, it has not been willing to supply that leadership. It shall therefore be argued that the changing nature of hegemony in world politics has set conditions that allow non-aligned middle powers and institutions greater scope for action and influence. The emergence of these issues has provided a scope for non-aligned middle powers, acting in accordance with their interests to play alternate leadership roles within an expanded scope for institutions, such as organisations, regimes and multilateralism, in addressing the interests of non-aligned states. Firstly in looking at an expanded role for organisations, the United States has increasingly been unwilling to play a leadership role within UN peacekeeping operations. The continuing importance of the neutrality of UN peacekeeping operations has provided a scope for nonaligned middle powers to play a burden-sharing role with the great powers in addressing the concerns of non-aligned states with regard to these operations. Secondly in looking at an expanded scope for regimes, the emergence of a regime in the issue of ozone depletion may provide a foundation to analyse how non-aligned middle powers may play a bridge-building role between North and South in the issue of climate change. Middle powers could therefore play this role in the absence of United States leadership within this issue. Thirdly, the role of the Cairns Group within the Uruguay Round in addressing non-aligned states’ interests of maintaining stable agricultural trade, can be seen as a model of small group multilateralism in bridging the divide between the major powers in issue specific areas.
17

Multi-instrumental auroral case studies at substorm conditions

Danielides, M. A. (Michael A.) 28 September 2005 (has links)
Abstract The general aim of the present study is to gain insight into physical mechanisms of some auroral forms on the basis of multi-instrumental measurements (satellites, rockets and ground-based magnetic and riometer instruments) in the vicinity of the auroras observed by ground-based all-sky cameras. One part of this work is related to the Auroral Turbulence II sounding rocket experiment. It was launched on February 11th, 1997, at 08:36 UT from Poker Flat Research Range, Alaska, into a moderately active auroral region after a substorm onset. This unique three-payload rocket experiment contained both electric and magnetic in the evening sector (21 MLT), auroral forms at the substorm recovery were investigated, providing details of the quiet and disturbed auroral densities and DC electric patches propagating along them like a luminosity wave. Those evening auroral patches and associated electric fields formed a 200-km spatially-periodic structure along the arc, which propagated westward at a velocity of 3 km s-1. The other part of this study describes ground signatures of dynamic substorm features observed by the IRIS imaging riometer, magnetometers and all-sky camera during late evening hours. The magnetometer data were consistent with the motion of upward data are used to estimate the intensity of FAC associated with these local current-carrying the excitation of the low-frequency turbulence in the upper ionosphere. As a result, a quasi-oscillating regime of anomalous resistivity on the auroral field lines can give rise to the burst-like electron acceleration responsible for simultaneously observed auroral forms and bursts of Pi1B pulsations.
18

Empirical Ionospheric Models: The Road To Conductivity

Edwards, Thomas Raymond 15 April 2019 (has links)
The Earth's polar ionosphere is a highly dynamic region of the upper atmosphere, and acts as the closure of the greater magnetospheric current system. This region plays host to many electrodynamic effects that impact terrestrial systems, such as power grids, railroads, and pipelines. These effects are fundamentally related to the currents, electric fields, and conductivity present in the polar ionosphere. Understanding and predicting the electrodynamics of this region is vital to being able to determine the physical impacts on terrestrial systems and provide predictions to government and commercial entities. Empirical models play a key role in the research and forecasting of the solar wind and interplanetary magnetic field's impact on the polar ionosphere, and is an active area of development and research. Recent interest in polar ionospheric conductivity has led to a community-wide campaign to develop our understanding of this portion of the electrodynamic system. Characterizing the interactions between the solar wind and the polar ionosphere is a difficult task, as the region of interest is highly data starved in many respects. In particular, satellite based data products are scarce due to being costly and logistically difficult. Recent advancements in data sources (such as the Swarm and CHAMP satellite missions) as well as continued research into the physical relationships between solar wind and interplanetary magnetic field drivers have provided the opportunity to develop new, novel tools to study this region of interest. In this dissertation, two polar ionosphere models are described in Chapters 3 and 4, along with the original research that their construction has produced in Chapter 1. These two models are combined to provide a foundation for future research in this area, which is described in Chapter 5. / Doctor of Philosophy / The Earth is subjected to a constant bombardment of solar particles and magnetic fields, known as the solar wind. Our planet’s geomagnetic field protects the atmosphere from this bombardment, and directs the plasma from the solar wind into the magnetic poles of the earth. This plasma flows through a region of the atmosphere called the ionosphere, where its energy is then dissipated. This energy has many impacts on the surface of the planet, including driving currents in power grids and generating auroral displays. The polar ionosphere is the fundamental connection between the solar wind and the planet, and being able to predict how and where this connection occurs is vital to studying its nature. This work describes two models of the plasma properties in the polar ionosphere, and provides some description of the original research that these models have garnered.
19

Aligned electrospun cellulose scaffolds coated with rhBMP-2 for both in vitro and in vivo bone tissue engineering

Zhang, X., Wang, C., Liao, M., Dai, L., Tang, Y., Zhang, H., Coates, Philip D., Sefat, Farshid, Zheng, L., Song, J., Zheng, Z., Zhao, D., Yang, M., Zhang, W., Ji, P. 13 February 2019 (has links)
Yes / Physical properties of scaffolds such as nanofibers and aligned structures have been reported to exert profound effects on the growth and differentiation of stem cells due to their homing-effect features and contact guidance. However, the biological function of aligned nanofiber utilized as bone-scaffold has not been rigorously characterized. In the present study, aligned electrospun cellulose/CNCs nanocomposite nanofibers (ECCNNs) loaded with bone morphogenic protein-2 (BMP-2) were used for the first time to investigate (1) in vitro osteogenic differentiation of human mesenchymal stem cells (BMSCs) and (2) in vivo collagen assembly direction and cortical bone regeneration. Aligned ECCNNs scaffolds loaded with BMP-2 possess good biological compatibility. The growth orientation of BMSCs followed the underlying aligned nanofibers morphology, accompanied with increased alizarin red stain, ALP activity and calcium content in vitro while, a rabbit calvaria bone defect model was used in an in vivo study. / This work was supported by Natural Science Foundation of China (NSFC) grants (31500789, 51433006, 51473100, 81870758 and 31871464), Chongqing Yuzhong District science and technology plan project grants (20170124), Chongqing Research Program of Basic Research and Frontier Technology (cstc2018jcyjAX0807, cstc2017jcyjBX0019 and cstc2017jcyjAX0020), Temple University Kornberg School of Dentistry research start-up funds, the RCUK China-UK Science Bridges Program through the Medical Research Council and the Engineering and Physical Sciences Research Council and Program for Innovation Team 1015 Building at Institutions of Higher Education (No. 1016 CXTDG201602006) funded by the Chongqing Municipal 1017 Education Commission of China in 2016
20

The changed meaning of non-alignment in international politics : the case of the NAM [1961-1992]

Wessels, Gideon Malherbe 06 1900 (has links)
This dissertation is a descriptive study in which the changed meaning of nonalignment in international politics between the years 1961 - 1992, is analysed. The concept non-alignment as manifested in four chronological phases of the Non-Aligned Movement {1960's, 1970's, 1980's, 1990/92] is analysed, compared and evaluated. The comparison shows that the meaning of non- alignment underwent a change in each of these four phases. It's meaning changed from a literal meaning in phases 1-3 [in which the focus shifted from being political to economic], to a symboric or figurative meaning in phase 4. The changes to the meaning of non-alignment came about mainly as a result of interaction with the international context and, to a lesser extent, due to the role of influential states in NAM. These changes were of critical importance for non-alignment to remain relevant and for NAM to be able to make a potential impact on an ever-changing world. / Political Sciences / M.A. (International Politics)

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