ETD at Indian Institute of Science
(528 recursos)
Repository of Theses and Dissertations of Indian Institute of Science, Bangalore, India. The repository has been developed to capture, disseminate and preserve research theses of Indian Institute of Science.
Mostrando recursos 1 - 20 de 33
1.
Imaging and Spectral Studies of Solar type I Noise Storms at Metric Wavelengths - Shanmugha Sundaram, G A
Type I noise storms constitute a sizeable fraction of the active-Sun component of solar radiation at meter wavelengths. The storms occur over a prolonged duration as intense, narrow-band spikes, superposed on a low-intensity broadband continuum, in the 30-400 MHz frequency range. Either component of the noise storm radiation has a very high degree of ordinary-mode circular
polarization (~ 100 %), and is widely believed to be generated by the plasma emission mechanism.
Existence of large sunspot groups or active region complexes, with a high degree of complexity and strength in the associated magnetic topology, have a remarkable spatio-temporal correlation to the occurance...
2.
Search for Northern Hemisphere Rapidly Oscillating Ap stars - V, Girish
Rapidly oscillating Ap (roAp) stars are cool, magnetic, chemically peculiar A-F type stars which exhibit high frequency oscillations similar to that of the famous five minute oscillations of Sun. These oscillations are interpreted as low degree (l<3), high order (n >10-30), non-radial p-mode oscillations. The periods of these pulsations lie in the range of 4-16 minutes with typical amplitudes of few milli-magnitudes
(< 8mmag) in the Johnson-B filter. More than a dozen roAp stars are multiperiodic, making them suitable for asteroseismology. The presence of high magnetic fields (of the order of few kG) in these stars gives us a chance...
3.
Studies of Static and Dynamic Multiscaling in Turbulence - Mitra, Dhrubaditya
The physics of turbulence is the study of the chaotic and irregular behaviour in driven fluids. It is ubiquitous in cosmic, terrestrial and laboratory environments. To describe the properties of a simple incompressible fluid it is sufficient to know its velocity at all points in space and as a function of time. The equation of motion for the velocity of such a fluid is the incompressible NavierStokes equation. In more complicated cases, for example if the temperature of the fluid also fluctuates in space and time, the NavierStokes equation must be supplemented by additional equations. Incompressible fluid turbulence is the...
4.
Methodological Developments In NMR Using Cross-correlations And Spatial Encoding - Bhattacharyya, Rangeet
This thesis aims at the methodological developments in Nuclear Magnetic Resonance
(NMR). The methodological developments in NMR has a long and successful history. The
present thesis attempts to contribute some novel methods in this direction.
This thesis restricts itself to two methodological developments, namely, (1) effects
of cross-correlations between the chemical shift anisotropy (CSA) and dipole-dipole
interactions in the relaxation of various nuclei and experiments which utilize spatial
encoding. The cross-correlation has been successfully utilized to investigate the anisotropic
motions of liquid crystals, and to understand the chemical shift anisotropy of fluorine atoms
of Fluorine substituted ring compounds. Spatial encoding schemes have been developed
to facilitate single scan measurements...
5.
Investigations Of Spin-Dynamics And Steady-States Under Coherent And Relaxation Processes In Nuclear Magnetic Resonance Spectroscopy - Karthik, G
The existence of bulk magnetism in matter can be attributed to the magnetic properties of the sub-atomic particles that constitute the former. The fact that the origin of these microscopic magnetic moments cannot be related to the existence of microscopic currents became apparent when this assumption predicted completely featureless bulk magnetic properties in contradiction to the observation of various bulk magnetic properties [1]. This microscopic magnetic moment, independent of other motions, hints at the existence of a hitherto unknown degree of freedom that a particle can possess. This property has come to be known as the "spin" of the particle....
6.
Light Scattering Investigations Near The Critical Point In Some Solvophobic Systems And The Design And Analysis Of A Microkelvin Thermostat For Critical Phenomena Studies - Unni, P K Madhavan
This thesis reports light-scattering experiments and visual investigations close to the critical point, in the solvophobic systems, 3-methylpyridine (3MP) + heavy water (D2O) + sodium bromide (NaBr) and methyl ethyl ketone (MEK) + water (W) + secondary butyl alcohol (sBA). The system 3MP + D2O + NaBr was chosen in order to throw more light on the reported crossover from mean-field to Ising-type of critical behaviour shown by this system and to investigate the existence of a mean-field tricritical point in it at an NaBr weight fraction of X = 0.1700, two issues that have been the subject of an...
7.
Carrier Mobility And High Field Transport in Modulation Doped p-Type Ge/Si1-xGex And n-Type Si/Si1-xGex Heterostructures - Madhavi, S
Modulation doped heterostructures have revolutionized the operation of field effect devices by increasing the speed of operation. One of the factors that affects the speed of operation of these devices is the mobility of the carriers, which is intrinsic to the material used. Mobility of electrons in silicon based devices has improved drastically over the years, reaching as high as 50.000cm2/Vs at 4.2K and 2600cm2/Vs at room temperature. However, the mobility of holes in p-type silicon devices still remains comparatively lesser than the electron mobility because of large effective masses and complicated valence band structure involved. Germanium is known to...
8.
X-Ray Crystallograhic Studies On 2',5', Cyclic And Modified Nucleotides - Singh, Umesh Prasad
This thesis presents the crystal structures of 2', 5', cyclic and modified nucleosides / nucleotides. Chapter I gives a brief account of the structural studies on 2', 5' and modified nucleotides. It also presents a short, summary of unusual nucleic acids structures studies on hydration patterns and metal ion interactions Nomenclature and conventions used for describing the conformatioNa1 features are presented. FiNa1ly, the crystallographic suite of programs used for processing the intensity data, structure solution, refinement and generating various diagrams are mentioned.
Chapter II describes the crystal structures of anhydrous and hydrated sodium salt of N6-methyl adenosine-S'-monophosphate. N6-AMP-A (anhydrous form) belongs...
9.
Studies On Growth And Physical Properties Of Certain Nonlinear Optical And Ferroelectric Crystals - Vanishri, S
Nonlinear optics and ferroelectrics have been recognized for several decades as promising fields with important applications in the area of opto-electronics, photonics, memory devices, etc. High performance electro-optical switching elements for telecommunications and optical information processing are based on the material properties. Hence, there is always a continuous search for new and better materials. In this thesis we have investigated the growth and physical properties of four crystals viz. two NLO and two ferroelectric crystals.
This thesis consists of eight chapters. The first chapter gives an overview of historical perspectives of nonlinear optical phenomenon, ferroelectricity and materials developed therein. The second...
12.
Thermal And Optical Properties Of Ge-Se Glass Matrix Doped With Te, Bi And Pb - Ganesan, R
During the last few years the scientific interest in chalcogenides glasses has been provoked on account of their properties and new application possibilities. These materials exhibit electrical and optical properties, which make them useful for several potential applications. Specifically the threshold and memory switching behavior and the infrared transmission of many of these glasses make the materials to be well suitable for use in memory devices and in fiber optics. Multicomponent glasses have been found to be more useful for many of these applications since the properties could be tailored for the specific uses. On account of this there has...
13.
Growth And Characterization Of Technologically Important Nonlinear Optical Crystals: Cesium Lithium Borate And Potassium Di-Deuterium Phosphate - Karnal, Ashwani Kumar
Present day advanced technologies heavily rely on one particular class of matter, i.e.
the crystals. It is the periodic nature of the atoms and the properties arising due to the periodicity in crystals that is exploited to meet various technological feats. The technological revolutions in the semiconductor, optics and communication industries are the examples. The anisotropy in the crystals gives them enhanced properties as required in the field of non-linear optics. The field of non-linear optics became practically a reality
after the invention of lasers. The coherent and monochromatic optical beams in the
visible and ultraviolet ranges are in high demand due to...
14.
Soft Matter : Routes To Rheochaos, Anomalous Diffusion And Mesh Phases - Ganapathy, Rajesh
Soft condensed matter (SCM) systems are ubiquitous in nature. SCM systems contain mesoscopic structures in the size range 10 nm to 1 am that are held together by weak entropic forces. These materials are therefore easily perturbed by external
fields such as shear, gravity and electric and magnetic fields and are novel systems
for studying non-equilibrium phenomena. The elastic constants of these materials are
? 109 times smaller than conventional atomic fluids and hence it is possible to measure the viscoelastic response of these materials using commercial instruments such as
rheometers. The relaxation time in SCM systems are of the order of milliseconds as
compared...
15.
A Radio Study Of Gas Loss Processes In Nearby Galaxies - Hota, Ananda
The work in this thesis involves detailed multi-frequency radio continuum
(from 325 MHz to 15 GHz) and Hi spectroscopic studies of a few represent
tative nearby galaxies which are experiencing gas-loss from their disks due
to different physical processes. These processes are starburst-driven superwind, active galactic nucleus (AGN) ?driven nuclear outflow, ram pressure stripping and tidal interactions. Gas-loss could a?ect the evolution of individual galaxies with age as well as their evolution with cosmic epoch. We
have made use of both the Giant Metrewave Radio Telescope (GMRT) and the Very Large Array (VLA) for our study.
Stars and gases are the two major constituents of...
16.
Thermal Fluctuation Spectroscopy And Its Application In The Study Of Biomolecules - Nagapriya, K S
The aim of this thesis is to study the energy fluctuations (leading to thermal fluctuations) during thermal and enzymatic denaturation of biological molecules and to study the variation in fluctuations between simple molecules like the DNA (which have only a secondary structure) to molecules with higher order structures and packaging. We have developed a new technique - Thermal Fluctuation Spectroscopy (TFS) to study these fluctuations.
The technique of Thermal Fluctuation Spectroscopy (TFS) is a combination of microcalorimetry and noise measurement techniques. The combination of these two powerful techniques has never been exploited before. In this technique any energy exchange between...
17.
Nature Of Criticality, Structuring, And Phase Behavior Of Complex Fluids - Bagchi, Debjani
This thesis is mainly concerned with some important properties of complex fluids, and how these properties are influenced by structures in the nano/mesoscopic scale. Short-range assembly of the constituent molecules results in an amazing variety of phase behavior in these systems. Liquid-liquid phase transitions, or transitions from a homogeneous(mixed) phase to an immiscible phase (two-phase coexistence), are the outcome of a competition between entropy and short-ranged attractive forces, and form an important part of this thesis. A rich phase behavior is uncovered by a detailed study of liquid-liquid phase transitions in a mixture of ethanol(E) and water(W), induced by the...
18.
X-ray Crystallographic Studies Of Designed Peptides, Self Assembling Pseudopeptides And Molecular Modeling - Hegde, Raghurama P
Structural studies of peptides has relevance for various applications, like, in de novo design of proteins, in designing better catalysts for organic synthesis, in structure based drug design, in the design and construction of synthetic protein mimics and in building novel materials via
supramolecular self assembly. Crystal structure determination of peptides is expected to provide information about their static structure, mode of aggregation, solvation and hydrogen bond interactions of the sequences in the solid state. Comparison and analysis of the related structures from the database analysis could provide information about sequence dependent
conformational features, which eventually would act as precursor for de...
19.
Theoretical Investigations Of Core-Level Spectroscopies In Strongly Correlated Systems - Gupta, Subhra Sen
Ever since the discovery of exotic phenomena like high temperature (Tc) superconductivity
in the cuprates and colossal magnetoresistance in the manganites, strongly correlated electron systems have become the center of attention in the field of condensed matter physics research. This renewed interest has been further kindled by the rapid development of sophisticated experimental techniques and tremendous computational power. Computation plays
a pivotal role in the theoretical investigation of these systems, because one cannot explain their complicated phase diagrams by simple, exactly solvable models. Among the plethora of experimental techniques, various kinds of high energy electron spectroscopies are fast gaining importance due to...
20.
Resistance Fluctuations And Instability In Metal Nanowires - Bid, Aveek
The principal aim of this thesis is to study the electrical transport properties of metal nanowires. Specifically, we have focussed on investigating the resistance fluctuations of Ag and Cu nanowires of diameters ranging from 15nm to 200nm and studied the instabilities that set in when the diameter is reduced below a certain range.
The nanowires were grown electrochemically inside polycarbonate and alumina templates. X-ray diffraction studies on the samples showed the presence of a HCP 4H phase in the Ag nanowires in addition to the usual FCC phase, which is seen in bulk Ag. The relative ratios of these two...
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