193 research outputs found
Synthesis, anticancer and antimicrobial potential of oxadiazoles
No full textOxadiazole is amongst the important classes of heterocyclic compounds that is the subject of intensive study of modern drug discovery. Synthesis of drugs containing oxadiazole moiety is attracting widespread attention due to their wide range of biological activities. In the present study, we developed a simple synthesis procedure for para-substituted 1,3,4-oxadiazole-2-thiones and their carboxymethyl derivatives based on the ring closure reactions of appropriate acid hydrazides with carbon disulphide. The synthesized compounds were characterized and evaluated for their anticancer and antimicrobial potential. The synthesized compounds significantly reduced the tumor weight and tumor cell count of Ehrlich ascites carcinoma (EAC) cells in mice. Almost all of the synthesized compounds showed significant antibacterial as well as antifungal activity. From the present investigation, it can be concluded that 1,3,4-oxadiazole compounds can potentially be developed into useful anticancer as well as antimicrobial agents. This study can prompt future researcher to synthesize a series of oxadiazole derivatives with the aim of finding newer anticancer and antimicrobial lead
Frustrated quantum magnets
No full textA class of Frustrated Quantum Magnets (FQM) is investigated using the Stochastic Series Expansion (SSE) Quantum Monte Carlo (QMC) method. Such a model is relevant to a class of rare earth tetraboride materials that display multi stepped magnetization plateaus under external magnetic field. The Shastry-Sutherland lattice was used to represent the arrangement of magnetic ions in these materials.
Previous studies showed a multistepped plateaus while plotting the z-magnetization against the external magnetic field. While many computer hours have been spent on supercomputers on trying to understand the multistepped phenomena, much has yet to be revealed.
In theory, we always choose the thermodynamic limit, but this is not possible in the real world. As such, we used Monte Carlo Simulations to assists us in understanding this multistepped phenomena. As computer hour is limited, we started using small system size, and increase it in factors related to the step level until we observe no change in the results.
The research done by Asst. Prof. Pinaki Sengupta and Keola Wierschem had produced planes of the ground state phase diagram. The diagrams showed the regions of plateaus and superfluidity state of the system. These diagrams give us an overview of the possible ground states with different parameters.
With Keola‟s help, I continued their work to produce the following plane of the ground state phase diagram. A different style in visualising the phase diagram is implemented for analyzing and categorizing regions of superfluidity and plateaus. We were also lucky enough to discover newfound plateaus in the initial stages of the project.Bachelor of Science in Physic
Suppression of gapless edge states in interaction driven topological insulators
No full textA topological insulator is a special class of material where the bulk of the material is gaped, exhibiting insulating properties, and the edges are gapless, exhibiting behaviours of a conductor due to one unpaired electron. This report seeks to investigate if there is any suppression of gapless edge states when lattice interactions are considered. These conditions were then simulated at ground state in an open-boundary, one-dimensional extended Peierls-Hubbard model at half-filling. A numerical method by the name of stochastic series expansion, a branch of Quantum Monte Carlo methods, is used to run the simulations for finite length models. The model considers electron-electron interactions and a finite range of electron-phonon coupling parameters. Firstly, spin stiffness is used as an indicator to observe the transition to Peierls state at ground temperature for closed boundary conditions at a critical phonon coupling value. This provides details about the critical phonon coupling values. Choosing an appropriate phonon coupling value based on the previous details, a comparison between odd length and even length chains were done at open boundary conditions. It was found that there is always suppression of gapless edge states for both even and odd length chain of sites.Bachelor of Science in Applied Physic
Energy dispersion relation of the antiferromagnetic Shastry-Sutherland lattice
No full textIn this project, we investigate the ground state properties of correlated electrons on the Shastry-Sutherland (SS) lattice, a 2-dimensional geometrically frustrated lattice which has attracted great interest in recent times in the context of quantum magnets. We first study the simplest possible model - the tight-binding model, for initial analysis. Further interaction terms are then added, so that one obtains the Hubbard model. Finally, spin-orbit coupling (between electrons and sites) terms are included, thus destroying spin-degeneracy. This is known as the Kane-Mele Hubbard model, which is expected to provide a rich variety of topological phases on the SS lattice. An important way to shed light on a system's electronic properties is to study its energy dispersion relation. This reveals various features, such as band structure, conductivity, and Hall conductance. The focus of this study would be to calculate the energy dispersion relations of each of the models mentioned. Some physical interpretations may be made about the physical observables, thus providing us with clues about its macroscopic behaviour. We start with a brief discussion of the mathematical framework used, and also an introduction to the respective models used; then, a brief discussion of the methodology and results is presented. The fi nal part of this report discusses the limitations of this study, and also provide suggestions on future
endeavours or possible extensions of the project.Bachelor of Science in Physic
Mott transition in hardcore Bose Hubbard model for honeycomb lattice
No full textThe purpose of this study is to learn how to use direct loop update Stochastic Series Expansion Quantum Monte Carlo simulation to observe Mott transition for a hard core bosonic system in a honeycomb lattice using a Bose-Hubbard model. Lattice occupancy is set at 1/2, and the simulation is run on 3 different lattice size, namely for L=4,6, and 8. During the simulation, the transition of the stiffness of the system is measured against the iterating parameter t/V, where t is the amplitude of the hopping component and V is the amplitude of the nearest neighbour potential. The critical point of the transition is then approximated from the intersection of the 3 transition curves.Bachelor of Science in Applied Physic
Digital Art and the Book Covers of Pinaki De as Response Text
No full textTraditional Literary Studies have often overlooked the transition of Book Cover illustration due to a disciplinary bias towards the written text over the visual narratives, dismissing them as mere commercial necessities. The paper intends to move beyond this prejudice by focusing on select covers designed by Pinaki De (B.T. Road/ The Hollow, The Garden of Solitude, Lost and Found, Mice in Men), through the analysis of the dynamics of text with their respective Cover, and show the Book Covers as intermedially remediating the text by the deployment of digital art that helps transcend the structural limitations of conventional art; as a result, they emerge as the first available visual reader response attached to the physicality of the text; for instance, in the Cover of Mice in Men, the effect of image morphing facilitated by digital pen and template establishes a visual connection between the visible eyebrow of the third panel and the mice of the first and final panel. The rendering bears no direct connection with the text but reflects the reader response of the illustrator; hence, a nuanced dialogue between Book Cover, the text, and the author emerges, intimating a new kind of visibility that is a symptomatic reflection of the decentralizing politics of the digital era, that, in scholarship and practice, intends to create “a new ‘we’ of community”. Thus, the paper claims a redefining of the significance of Book Covers in contemporary literary discourse and proclaims the liminal space between digital and humanities as more collegial and humanitarian, than ever before
Neel to spin-Peierls transition in the ground and excited state of a quasi-1D Heisenberg model coupled to bond phonons.
No full textThe spin-Peierls transtion in the ground state (quantum phase transition) and excited state(thermal phase transition) of a quasi-1D Heisenberg model is investigated using the stochastic series expansion quantum monte carlo method. The transition from a gapless Neel state to a spin-gapped Peierls state is studied in the parameter space spanned by spatial anisotropy, inter-chain coupling and spin-lattice coupling. It is found that for any inter-chain coupling, the transition to a dimerized Peierls state only occurs when the spin-lattice coupling exceeds a finite, non-zero critical value.Bachelor of Science in Physic
Computational study on 1D quantum spin chain
No full textDue to the large quantum fluctuation, there are many 1D quantum magnets in real life which exhibit exotic phases, such as quantum spin liquid state in the ground state of Cs4CuSb2Cl12 and PbNi2V2O8 [2] and SrNi2V2O8 [3] whose ground state is close to the phase boundary between Haldane phase (which is a fourfold-degenerate edge state) and Ising antiferromagnetic phase.
Apart from that, there are many powerful numerical methods which prove more efficient than analytical approach when studying 1D spin chain, such as Quantum Monte Carlo method, renormalization group and field theoretic method. The abundance of numerical method enables physicist to investigate quantum spin chain in more details. For instance, they can study the emergence of quantum phase due to the interplay of interactions, such as Heisenberg interaction, geometric frustration and Dzyalonshinskii-Moriya interaction.
This project aims to demonstrate different kinds of numerical method to obtain and
study the ground state of different 1D models.Bachelor of Science in Physic
Spin-Peierls transition in 2D Heisenberg model with bond phonons.
No full textTwo kinds of possible dimerization patterns of Spin-Peierls transition in a 2D spin-1/2 Heisenberg model antiferromagnetic coupled to bond phonons with variable inter-chain coupling strength, corresponding to wave vectors Q=(π,0) andQ=(π,π), are investigated by using the Stochastic Series Expansion Quantum Monte Carlo method. The system is simulated by spin-1/2 Heisenberg Model with Nearest-Neighbor with inter-chain antiferromagnetic coupling. It is found that, at the same temperature, the (π, π) dimerization pattern is reached at a weaker inter-chain coupling than the (π, 0) dimerization pattern. At the same temperature and the same inter-chain coupling strength, when the system reaches the dimerization state, the energy of the (π, 0) pattern is lower, which means in this Model, the (π, 0) dimerization pattern is more stable.Bachelor of Science in Physic
Computational studies on the static and dynamical properties of one dimensional integer spin quantum magnets
No full textOne dimensional quantum magnets have always been an active area of research due to
their experimental realizability and the rich physics that they offer. By including geometrical
frustration and additional interactions, it leads to even more novel and exotic
quantum phases. In this thesis, we present the results of our investigations conducted by
extending the quantum systems to spin–1. We conducted static, topological and dynamical
calculations numerically on the spin–1 Heisenberg chain with Dzyaloshinskii–Moriya
interaction in a uniform magnetic field in the form of a spin–1 Heisenberg chain in a helical
magnetic field as well as the spin–1 Heisenberg model on the spin diamond and
orthogonal dimer lattices. For the spin–1 Heisenberg chain in a helical field, we obtained
the phase diagram using the density matrix renormalization group method and
showed conclusively that the helical field destroys any topological order. We also obtained
the dynamical spin structure factor spectra to study the magnon band structures
and the softening of the modes near phase transitions. We then investigated the spin–1
Heisenberg model on the spin diamond and orthogonal dimer lattices using both exact
diagonalization and the density matrix renormalization group method. We obtained the
phase diagrams for both systems and explicitly calculated the magnetization, static spin
structure and topological order of the different phases. Similar to the spin–1 Heisenberg
chain in a helical magnetic field, we also obtained the dynamical spin structure factor
spectra to study the characteristics of the lowest excitation occurring in both quantum
systems.Doctor of Philosoph
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