Investigations on Broadband Plannar Monoplole Antennas with Truncated Ground Plane

The space constraints on wireless gadgets is a challenge to antenna designers as the ground plane dimensions of the printed monopole significantly affect s the antenna characteristics.Investigations on ground plane truncations have led to the development of an extremely broad band printed monopole antenna.Omnidirectional radiation characteristics with moderate gain makes this antenna highly suitable for mobile/wireless applications .This thesis also highlights the development of UWB printed antenna along with design equations .Optimum ground plane dimensions for compact antenna applications,folding technique for miniaturization and double folding for dual band application are the other highlights of this thesis.

Synthesis and Photochemistry of a few Olefin appended Dibenzobarrelenes and Bisdibenzobarrelenes

The thesis entitled: ‘Synthesis and Photochemistry of a few Olefin appended Dibenzobarrelenes and Bisdibenzobarrelenes’ is divided into 5 chapters.In Chapter 1, the fundamental concepts of Diels-Alder reaction, di-r:methane rearrangement and energy transfer process in organic photochemistry is discussed.Chapter 2 presents the synthesis of 9-olefin appended anthracenes and bisanthracenes. The target of synthesising various bridgehead olefin appended dibenzobarrelenes and some novel bisdibenzobarrelenes, led us to the synthesis of the appropriate alkenylanthracenes and bisanthracenes as precursor molecules. Diels-Alder reaction was the synthetic tool for the preparation of the target olefin appended dibenzobarrelenes and bisdibenzobarrelenes. This chapter attempts to throw light on our endeavours in synthesising the various 9-alkenylanthracenes and bisanthracenes.Chapter 3 deals with the synthesis of olefin appended dibenzobarrelenes and bisdibenzobarrelenes. Ever since the discovery of di-It-methane rearrangement dibenzobarrelenes, tailored with dijferent substituents at various positions have always been a tool to photochemists in unravelling the mechanisms of light induced reactions. Our intention of analysing the role of a It-moiety at the bridgehead position of the dibenzobarrelene, was synthetically envisaged via the Diels-Alder reaction. Bisdibenzobarrelenes were synthesised through tandem Diels-Alder reaction. Various alkenylanthracenes and bisanthracenes were employed as dienes and the dienophiles used were dimethyl acetylenedicarboxylate and dibenzoylacetylene. In this chapter, we report our venture in synthesising the various olefin appended dibenzobarrelenes and bisdibenzobarrelenes. Chapter 4 describes the preliminary time-resolved fluorescence studies of some olefin appended dibenzobarrelenes and bisdibenzobarrelenes.To understand the primary and secondary physicochemical processes in a photochemical reaction it is necessary to characterise the excited states and the transient intermediates during their short lifetime. A number of methods developed on the basis of the physical properties of the transient species are available for their detection. Time-correlated single-photon counting technique has been utilised in the present study of the excited states of olefin appended dibenzobarrelenes and bisdibenzobarrelenes. To understand the primary and secondary physicochemical processes in a photochemical reaction it is necessary to characterise the excited states and the transient intermediates during their short lifetime. A number of methods developed on the basis of the physical properties of the transient species are available for their detection. Time-correlated single-photon counting technique has been utilised in the present study of the excited states of olefin appended dibenzobarrelenes and bisdibenzobarrelenes.Chapter 5 portrays the photochemistry of olefin appended dibenzobarrelenes and bisdibenzobarrelenes. Dibenzocyclooctatetraene and dibenzosemibullvalene are the photoproducts obtained respectively through the singlet excited state and the triplet excited state of dibenzobarrelenes. Chemical literature shows evidences of the photoreactivity of dibenzobarrelenes generating both the singlet and triplet mediated photoproducts, in a single photoreaction. Our research target in synthesising various bridgehead olefin appended dibenzobarrelenes and bisdibenzobarrelenes, was based on the perception that olefins are eflicient triplet quenchers, thereby quenching intramolecularly the triplet excited state of the barrelenes. A It-moiety at the bridgehead position of the dibenzobarrelene, creates a tetra tr-methane system, which similar to a 6li—7l' or tri-tr-methane systems, could be the fertile ground for interesting photochemical rearrangements. Our attempts in deciphering the photochemistry of the olefin appended dibenzobarrelenes and bisdibenzobarrelenes is the substance of this chapter.

Studies on the Solvent Dependence in the Reaction of a Few (Anthracen-9-yl)MethyLamines and Sulfanes with Reactive Acetylenes

The thesis entitled ‘Studies on the Solvent Dependence in the Reaction of a Few (Anthracen-9-yl)methylamines and Sulfanes with Reactive Acetylenes’ is divided into six chapters. ln Chapter l a general survey of electron transfer reactions, Diels-Alder reactions and Michael-type additions is presented. A detailed discussion on the synthesis of several (anthracen-9-yl)methylamines is presented in Chapter 2. In Chapter 3, results of preliminary photophysical studies on a few (anthracen-9yl) methylamines are compiled. A detailed discussion on extensive examination of dependence in the reaction of (anthracen-9-yl)methylamines with reactive acetylenes is presented Chapter 4. Details on the synthesis and reaction of a few (anthracen-9-yl)methylsulfanes with DMAD are described in Chapter 5.

Ground-state self-consistent calculation of quantum dots under magnetic fields: Addition spectrum

A density-functional self-consistent calculation of the ground-state electronic density of quantum dots under an arbitrary magnetic field is performed. We consider a parabolic lateral confining potential. The addition energy, E(N+1)-E(N), where N is the number of electrons, is compared with experimental data and the different contributions to the energy are analyzed. The Hamiltonian is modeled by a density functional, which includes the exchange and correlation interactions and the local formation of Landau levels for different equilibrium spin populations. We obtain an analytical expression for the critical density under which spontaneous polarization, induced by the exchange interaction, takes place.

Studies on nonlinear dynamics of certain reaction systems

The nonlinear dynamics of certain important reaction systems are discussed and analysed in this thesis. The interest in the theoretical and the experimental studies of chemical reactions showing oscillatory dynamics and associated properties is increasing very rapidly. An attempt is made to study some nonlinear phenomena exhibited by the well known chemical oscillator, the BelousovZhabotinskii reaction whose mathematical properties are much in common with the properties of biological oscillators. While extremely complex, this reaction is still much simpler than biological systems at least from the modelling point of view. A suitable model [19] for the system is analysed and the researcher has studied the limit cycle behaviour of the system, for different values of the stoichiometric parameter f, by keeping the value of the reaction rate (k6) fixed at k6 = l. The more complicated three-variable model is stiff in nature.

Coastal and ground water pollution in Kavaratti island, Lakshadweep sea

The tiniest Union territory of India, Lakshadweep, is an archipelago, with an area of 32 Sq. km. consisting of 12 atolls, three reefs and five submerged banks, lies between 8° and 12°30'N latitudes and 71° and 74" E longitudes. It is one of the most important and critical territories of India from economic and defence point of view. Specialised environment having typical geological set up, Lakshadweep is ecologically sensitive to even slight climatic or anthropogenic interference. Pollution of coastal seas, over exploitation and contamination of the fresh water sources are thus become great concerns to the existence of the island. Typical geological set up and interference cause threat to the ecology of the fragile environment and resources of the island as well as its resources. Marine pollution and ground water contamination are concerns in this regard. Even though attentions were made to assess the physico—chemical and bacteriological status of the marine and groundwater systems separately, an integrated approach has not been evolved. The present study with its broad objectives is attempted for an integrated assessment of microbiological, physicochemical and biological characteristics of the surrounding seawater and microbiological and physico—chemical characteristics of the ground water in Kavaratti island. The entire study has been organised in 4 chapters

Ground- and excited-state properties of M-center oxygen vacancy aggregates in the bulk and the surface of MgO

Aggregates of oxygen vacancies (F centers) represent a particular form of point defects in ionic crystals. In this study we have considered the combination of two oxygen vacancies, the M center, in the bulk and on the surface of MgO by means of cluster model calculations. Both neutral and charged forms of the defect M and M+ have been taken into account. The ground state of the M center is characterized by the presence of two doubly occupied impurity levels in the gap of the material; in M+ centers the highest level is singly occupied. For the ground-state properties we used a gradient corrected density functional theory approach. The dipole-allowed singlet-to-singlet and doublet-to-doublet electronic transitions have been determined by means of explicitly correlated multireference second-order perturbation theory calculations. These have been compared with optical transitions determined with the time-dependent density functional theory formalism. The results show that bulk M and M+ centers give rise to intense absorptions at about 4.4 and 4.0 eV, respectively. Another less intense transition at 1.3 eV has also been found for the M+ center. On the surface the transitions occur at 1.6 eV (M+) and 2 eV (M). The results are compared with recently reported electron energy loss spectroscopy spectra on MgO thin films.

High-momentum proton removal from 16 O and the (e,e'p) cross section

The cross section for the removal of high-momentum protons from 16O is calculated for high missing energies. The admixture of high-momentum nucleons in the 16O ground state is obtained by calculating the single-hole spectral function directly in the finite nucleus with the inclusion of short-range and tensor correlations induced by a realistic meson-exchange interaction. The presence of high-momentum nucleons in the transition to final states in 15N at 60¿100 MeV missing energy is converted to the coincidence cross section for the (e,e¿p) reaction by including the coupling to the electromagnetic probe and the final state interactions of the outgoing proton in the same way as in the standard analysis of the experimental data. Detectable cross sections for the removal of a single proton at these high missing energies are obtained which are considerably larger at higher missing momentum than the corresponding cross sections for the p-wave quasihole transitions. Cross sections for these quasihole transitions are compared with the most recent experimental data available.

Delta(1232) isobar excitations and the ground state of nuclei

The influence of Delta isobar components on the ground-state properties of nuclear systems is investigated for nuclear matter as well as finite nuclei. Many-body wave functions, including isobar configurations and binding energies, are evaluated employing the framework of the coupled-cluster theory. It is demonstrated that the effect of isobar configurations depends in a rather sensitive way on the model used for the baryon-baryon interaction. As examples for realistic baryon-baryon interactions with explicit inclusion of isobar channels we use the local (V28) and nonlocal meson-exchange potentials (Bonn2000) but also a model recently developed by the Salamanca group, which is based on a quark picture. The differences obtained for the nuclear observables are related to the treatment of the interaction, the pi-exchange contributions in particular, at high momentum transfers.

Quasilocal density functional theory and its application within the extended Thomas-Fermi approximation

In this paper we propose a generalization of the density functional theory. The theory leads to single-particle equations of motion with a quasilocal mean-field operator, which contains a quasiparticle position-dependent effective mass and a spin-orbit potential. The energy density functional is constructed using the extended Thomas-Fermi approximation and the ground-state properties of doubly magic nuclei are considered within the framework of this approach. Calculations were performed using the finite-range Gogny D1S forces and the results are compared with the exact Hartree-Fock calculations