Browsing by Author "Nayak, Biswajit"

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    Dynamic stability of Magnetorheological elastomer Based Sandwich Beams
    (2013) Nayak, Biswajit
    The work presented in this thesis is concerned with the theoretical and experimental investigation of the dynamic characteristics and stability of the magnetorheological elastomer (MRE) based sandwich beams subjected to periodic axial load and magnetic field. An extensive literature review has been presented which covers the use of various types of MREs for sandwich beam construction, free and forced vibration and stability analysis of sandwich beams. It is observed that a few works are available on dynamic characteristics and stability of MRE embedded sandwich beam and hence an attempt has been made to study theoretically and experimentally the above mentioned system. Initially, using classical sandwich beam theory, extended HamiltonDs principle along with generalized GalerkinDs method the governing equation of motion of a sandwich beam with MRE embedded viscoelastic core and conductive skins has been derived when it is subjected to static magnetic field. The effects of magnetic field, core thickness, percentage of iron particles and carbon blacks on the free vibration responses and regions of parametric instability have been studied for various end conditions of the sandwich beam. The same system is studied by applying time varying magnetic field and periodic axial load. The system is reduced to that of a parametrically excited system with two frequency excitation. Method of multiple scales is used to study the stability boundaries for various resonance conditions with simply supported and clamped free boundary conditions. As the classical methods can only be used for systems with simple geometry and classical boundary conditions, finite element method (FEM) has been employed to study the vibration problems in general purpose MRE embedded sandwich beam with static magnetic field. Using FEM the dynamic characteristics and stability of...
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    Urea Functionalized Acyclic Receptors: Anion Coordinated Hydrogen Bonded Supramolecular Self-assembly
    (2021) Nayak, Biswajit
    The thesis entitled “Supramolecular Self-assemblies of Hydrogen Bonding Acyclic Scaffolds: Anion Coordination by Urea Functionalized Receptors” have been divided into five chapters established on the results of experimental work performed during the research period. The first chapter provides a brief introduction to ‘supramolecular host-guest chemistry’ regarding the recognition of anions/hydrated anions within the preorganized cavity or self-assemblies of artificial acyclic receptors, isomeric with respect to either terminal substituents or preliminary materials. It also summarizes general introduction and literature survey in context with the thesis title, which is documented nicely. The citation of the previously reported work in this field and general idea for the thesis objective is described nicely. Chapter 2 gives a comprehensive report of the various reagents used in the synthesis of the receptors, their synthetic pathways, crystallization details, binding study and specifications of analytical instruments employed in the characterization of designed and synthesized free receptors and their various anion complexes with anions/hydrated-anions and anionic associations are represented thoroughly. The chapter 3 describes the design and syntheses of two electron-rich naphthyl rings containing bisurea receptor derived from ortho (L1) and meta (L2)-phenylenediamine moiety for investigating their anion coordination behavior. Receptor L1 self-assembled in the presence of organic terephthalate anion into a dimeric pseudo-capsular host-guest assembly sealed by tetrabutylammonium counter cation. Chapter 4 deals with three linear flexible bisurea receptors (L3-L5) with different terminal substituents have been synthesized for a comprehensive analysis of host-guest binding propensity in their neutral form. The highlight of the chapter 5 is that with the cyano group as a terminal substituent, three positional isomeric bis-urea receptors (L6-L8) have been synthesized for extensive analysis of host–anion binding propensity in their neutral form.