24 research outputs found
Polymer dynamics and fluctuations probed with fluorescence methods
No full textThe arc of the thesis is direct measurement of polymer chain properties with potent fluorescence methods imported from other interdisciplinary sciences and applied successfully to polymer physics problems for the first time.
The focus is an important theme in equilibrium polymer physics - chain structure and dynamics at solid-liquid interfaces and confined geometries, respectively. The role of polymer dynamics and fluctuations on the topological confinement formed by entanglement strands in a polymer solution, as experienced by a particle of comparable size is also investigated. These questions are fundamental in many scientific and technical applications, including adhesion, interdiffusion, friction, the mechanical behavior of composite and nanocomposite materials, and functional properties of other kinds. The experimental investigations involve development of novel fluorescence techniques of spectroscopy, microscopy and image analysis with single molecule sensitivity and/or single particle accuracy. Use of these techniques allow access to phenomena occurring at a wide range of length scales and time scales, characteristic of problems in macromolecular physics. Single particle tracking experiments also show advantages of unearthing distribution of individual particle dynamics within an ensemble.Item withdrawn by Laura Spradlin ([email protected]) on 2014-11-13T16:56:56Z
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University of Illinois Theses & Dissertations (ID: 1)
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Temperature dependent photoluminescence in self assembled InAs quantum dot arrays
No full textIn this paper we investigate the competing effects of thermally assisted hopping and radiative recombination of disorder induced spatially localized excitons on the temperature dependent PL spectrum of a self assembled InAs quantum dot array on GaAs. The stationary photoluminescence spectrum due to the lowest exciton state is calculated from a Monte Carlo simulation. We have also included the effect of the narrowing of the band gap with the increase of temperature. Our results on variation of the peak position and linewidth of the PL spectrum with temperature are in agreement with existing experimental results on InAs/GaAs dot arrays
Ferromagnetism of anderson localized electrons: application to cluster compounds
No full textA study of the electrical transport and magnetic properties of a series of cluster compounds with the generic formula A0.5M2X4 suggests that the electrons at the Fermi surface are localized, and the ferromagnetism seen in these compounds arises from these electrons. The magnetism of these compounds shows some features characteristic of itinerant models and others which are characteristic of localized models. We construct a model which has a nondegenerate band of localized states with on-site repulsion. Further, the singly occupied states interact via direct exchange interaction which is ferromagnetic. Using a mean-field approximation we calculate the various magnetic properties, which are in qualitative accord with the observed behavior. In particular, we find that the single-particle excitations play a dominant role in the magnetism of these compounds, even though the electrons are localized. We also analyze the spin-wave excitations in this model and discuss their effect on low-temperature thermodynamics
Giant primary ovarian fibrosarcoma: Case report and review of pitfalls
No full textPrimary ovarian fibrosarcomas are very uncommon neoplasms; less than one hundred cases have been reported. Diagnosis can be difficult to establish and other similar appearing mesenchymal lesions must be ruled out. A 23 year old nulliparous woman presented with a huge right ovarian tumor (25 × 17 × 12 cm). Ultrasonography guided aspiration was performed and a strong possibility of fibrosarcoma was suggested based on cytomorphological findings. No epithelial element was noted. She underwent surgical excision which confirmed the diagnosis of primary ovarian fibrosarcoma (the largest till date to our knowledge). Immunohistochemical analyses showed vimentin and CD 34 positivity. We speculate that ovarian fibrosarcoma at the preoperative examination might be considered in the differential diagnosis whenever a unilateral, heterogeneous, largely round solid ovarian lesion is detected
Role of defects in transport through a quantum dot single electron transistor
No full textThe effect of a single dotlike defect on the transport through a quantum dot single electron transistor weakly coupled to external leads is studied. It is found that the conductance profile is changed significantly by the quantum mechanical tunneling between the dot and the defect and the interactions between them, both of which are dependent on the distance between the dot and the defect, as also by the morphology of the defect. In particular, we find that even a very small strength of interdot interaction has a major influence on the transport and must be taken into account in device fabrication
Role of defects in transport through a quantum dot single electron transistor
No full textThe effect of a single dotlike defect on the transport through a quantum dot single electron transistor weakly coupled to external leads is studied. It is found that the conductance profile is changed significantly by the quantum mechanical tunneling between the dot and the defect and the interactions between them, both of which are dependent on the distance between the dot and the defect, as also by the morphology of the defect. In particular, we find that even a very small strength of interdot interaction has a major influence on the transport and must be taken into account in device fabrication
Use of eyring equation to explore the frictional responses of a -CF3 and a -CH3 terminated monolayers self assembled on silicon substrate
No full textLateral force microscopy is used to measure the frictional forces generated in sliding a silicon nitride tip on perflurooctyl trichlorosilane (FOTS) and octadecyltrichlo rosilane (ODTS) monolayers self-assembled (SAM) on silicon wafer. The work is motivated by a need to rationalize the high friction of FOTS in comparison to that found for ODTS, inspite of the former having a low surface energy compared to that of the latter. Having first established that the tribology here is a thermally activated process, we use the Eyring equation to estimate the energetic barrier height to sliding motion, system activation energy, shear coordination and pressure activation volumes.For a molecular species when the velocity and temperature are unchanged in a sliding experiment and the activation energy remains unchanged the change in shear coordination with increasing normal load controls the friction coefficient. In comparing the performance of the two test molecules the friction coefficient of theFOTS is found to be three times greater than that of the ODTS; the corresponding difference in barrier height isabout 10%. Our results indicate that when the two molecules are well ordered, the shear coordination modulates the frictional differential but it is the difference in their system activation energy,principally determined by electrostatic repulsion between the neighbouring molecules which is a dominant influence on their friction differential
Design of FPGA based horizontal velocity computation and image storage unit for lunar lander
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