Doctor of Philosophy

dissertationIn this dissertation, we present methods for intuitive telemanipulation of manipulators that use piezoelectric stick-slip actuators (PSSAs). Commercial micro/nano-manipulators, which utilize PSSAs to achieve high precision over a large workspace, are typically controlled by a human operator at the joint level, leading to unintuitive and time-consuming telemanipulation. Prior work has considered the use of computer-vision-feedback to close a control loop for improved performance, but computer-vision-feedback is not a viable option for many end users. We discuss how open-loop models of the micro/nano-manipulator can be used to achieve desired end-effector movements, and we explain the process of obtaining open-loop models. We propose a rate-control telemanipulation method that utilizes the obtained model, and we experimentally quantify the effectiveness of the method using a common commercial manipulator (the Kleindiek MM3A). The utility of open-loop control methods for PSSAs with a human in the loop depends directly on the accuracy of the open-loop models of the manipulator. Prior research has shown that modeling of piezoelectric actuators is not a trivial task as they are known to suffer from nonlinearities that degrade their performance. We study the effect of static (non-inertial) loads on a prismatic and a rotary PSSA, and obtain a model relating the step size of the actuator to the load. The actuator-specific parameters of the model are calibrated by taking measurements in specific configurations of the manipulator. Results comparing the obtained model to experimental data are presented. PSSAs have properties that make them desirable over traditional DC-motor actuators for use in retinal surgery. We present a telemanipulation system for retinal surgery that uses a full range of existing disposable instruments. The system uses a PSSA-based manipulator that is compact and light enough that it could reasonably be made head-mounted to passively compensate for head movements. Two mechanisms are presented that enable the system to use existing disposable actuated instruments, and an instrument adapter enables quick-change of instruments during surgery. A custom stylus for a haptic interface enables intuitive and ergonomic telemanipulation of actuated instruments. Experimental results with a force-sensitive phantom eye show that telemanipulated surgery results in reduced forces on the retina compared to manual surgery, and training with the system results in improved performance. Finally, we evaluate operator efficiency with different haptic-interface kinematics for telemanipulated retinal surgery. Surgical procedures of the retina require precise manipulation of instruments inserted through trocars in the sclera. Telemanipulated robotic systems have been developed to improve retinal surgery, but there is not a unique mapping of the motions of the surgeon's hand to the lower-dimensional motions of the instrument through the trocar. We study operator performance during a precision positioning task on a force-sensing phantom retina, reminiscent of telemanipulated retinal surgery, with three common haptic-interface kinematics implemented in software on a PHANTOM Premium 6DOF haptic interface. Results from a study with 12 human subjects show that overall performance is best with the kinematics that represent a compact and inexpensive option, and that subjects' subjective preference agrees with the objective performance results

The sedimentation of flexible filaments

The dynamics of a flexible filament sedimenting in a viscous fluid are explored analytically and numerically. Compared to the well-studied case of sedimenting rigid rods, the introduction of filament compliance is shown to cause a significant alteration in the long-time sedimentation orientation and filament geometry. A model is developed by balancing viscous, elastic, and gravitational forces in a slender-body theory for zero-Reynolds-number flows, and the filament dynamics are characterized by a dimensionless elasto-gravitation number. Filaments of both non-uniform and uniform cross-sectional thickness are considered. In the weakly flexible regime, a multiple-scale asymptotic expansion is used to obtain expressions for filament translations, rotations, and shapes. These are shown to match excellently with full numerical simulations. Furthermore, we show that trajectories of sedimenting flexible filaments, unlike their rigid counterparts, are restricted to a cloud whose envelope is determined by the elasto-gravitation number. In the highly flexible regime we show that a filament sedimenting along its long axis is susceptible to a buckling instability. A linear stability analysis provides a dispersion relation, illustrating clearly the competing effects of the compressive stress and the restoring elastic force in the buckling process. The instability travels as a wave along the filament opposite the direction of gravity as it grows and the predicted growth rates are shown to compare favorably with numerical simulations. The linear eigenmodes of the governing equation are also studied, which agree well with the finite-amplitude buckled shapes arising in simulations

Hashimoto’s thyroiditis-a tertiary level hospital based study

Background: Hashimoto’s disease is a chronic, autoimmune form of thyroiditis and is one of the most common causes for hypothyroidism. Many studies have found an association between Hashimoto’s thyroiditis and various other thyroid pathologies, including cancers. The objectives of the study were to look for any association between Hashimoto’s thyroiditis and other forms of thyroid diseases and to analyse the pattern of patients treated with Hashimoto’s thyroiditis.Methods: This was a retrospective study conducted at a tertiary care centre from December 2008 to January 2014. Patients with Hashimoto’s thyroiditis confirmed by histology were selected as the cases. Their clinical and biochemical data and post-operative histopathological reports were collected and analysed.Results: 300 patients who underwent thyroidectomy were found to have a diagnosis of Hashimoto’s thyroiditis. 97.33% of the patients were females. Maximum patients belonged to the 31-40 age group. Of the 300 patients, 61.67% had other associated pathologies. The maximum association was with colloid goiters, followed by adenomas and malignancies. Among the malignancies, 80.65% were papillary cancers while the rest were follicular cancers. There were no cases of other malignancies associated with Hashimoto’s thyroiditis.Conclusions: Hashimoto’s thyroiditis is fairly common in the studied population, mostly among females. It is associated with other thyroid pathologies including differentiated cancers. Lymphoma is not found to be associated with Hashimoto’s disease in our population. Hashimoto’s thyroiditis thus forms a major share of goiters leading to thyroidectomy in Indian population. However, the decision to operate should be primarily governed by the associated cytology

Copolymers and Blends of Methyl Acrylate and Acrylic Isobutyl POSS Nanomaterials

Ultra-thin polymer films attached to solid substrates (supported films) have attracted significant interest in recent years. Supported films are used in the design of advanced materials like photoresists, lubricants and other electronic devices. Glass transition temperatures (Tgs) of supported polymer films have also been of significant interest. The Tg has been shown to depend on the thickness of the polymer film on the surface and the inherent nature of the surface. The effect of end-grafting of a polymer chain to a surface, on the Tg of the polymer has been studied previously.1 Reports on the study of glass transition behaviors of different types of supported polymer films on substrates of a varying nature exist. These studies include investigations of the dependence of Tg on various parameters like film thickness, nature of the substrate, molecular architecture, stereochemistry of the polymer and interfacial interaction effects.10-15 in this preprint, we report the study of the Tg behavior of poly(methyl acrylate) (PMA) chains covalently bonded to silica using a silane coupling agent. Several PMA-silica composite samples with different relative amounts (low, medium and high) of PMA attached to the silica were synthesized and the Tg of the attached PMA in each composite was determined using modulated differential scanning calorimetry (MDSC). The attached PMA, in the composite samples, exhibited interesting glass-transition behavior

Studying the variability of fluorescence emission and the presence of clumpy wind in HMXB GX 301−-2 using XMM-Newton

We present the results from an analysis of data from an \textit{XMM-Newton} observation of the accreting high mass X-ray binary pulsar GX 301$-$2. Spectral analysis in the non-flaring segment of the observation revealed that the equivalent width of the iron fluorescence emission is correlated with the observed absorption column density and the ratio of the iron K$\beta$ and K$\alpha$ line strength varied with the flux of the source. Coherent pulsations were detected with the spin period of the pulsar of 687.9$\pm$0.1 s, and a secondary pulsation was also detected with a period of 671.8$\pm$0.2 s, most prominent in the energy band of the iron line. At the spin period of the neutron star, the pulsation of the iron line has a low amplitude and the profile is different from the continuum. Pulse phase-resolved spectroscopy also revealed pulsations of the iron emission line during the non-flaring segment of the light curve. At the secondary period, both the iron line and the continuum have nearly identical pulse fraction and pulse profile. The additional periodicity can be attributed to the beat frequency between the spin of the neutron star and the Keplerian frequency of a stellar wind clump in retrograde motion around the neutron star. Reprocessed X-ray emissions originating from the clump can produce the observed secondary pulsations both in the continuum and the iron fluorescence line. The clump rotating around the neutron star is estimated to be approximately five lt-s away from the neutron star.Comment: 11 pages, 15 figures, Accepted for publication in Monthly Notices of the Royal Astronomical Societ

Moisture dependent physical properties of maize (PMH-1)

Physical properties of maize were evaluated as a function of moisture content. The obtained data provide help in the designing of post-harvest handling machinery. In the moisture range of 10–18% wet basis (w.b.), the length of the rewetted grain increased from 10.01 to 10.65 mm, width increased from 8.57 to 8.70 mm, thickness ranged from 4.63 to 4.97 mm, geometric mean diameter (GMD) increased from 7.34 to 7.67 mm, sphericity increased from 0.72 to 0.73, thousand kernel weight (TKW) increased from 258.1 to 287.9 g, bulk density decreased from 591.6 to 554.2 kg m−3, true density increased from 1194.9 to 1267.2 kg m−3, porosity increased from 52.61 to 56.27%, hardness decreased from 293.75 to 228.04 N, initial cracking force decreased from 190.11 to 137.35 N and area ranges from 55.09 to 36.58 Nmm. In the same moisture range the angle of repose varied from 23.36 to 28.55 for grain. Lightness (L) of grain ranges from 62.82 to 59.26, a value (red-green axis) ranges from 13.97 to 8.96, b value (yellow-blue axis) ranges from 31.05 to 26.19 and hue angle (z%) decreased from 14.59 to 14.06 with increase in moisture content of grain from 10 to 18% w.b