External Electric Field Mediated Quantum Phase Transitions in One-Dimensional Charge Ordered Insulators: A DMRG Study

We perform density matrix renormalization group (DMRG) calculations extensively on one-dimensional chains with on site (U) as well as nearest neighbour (V) Coulomb repulsions. The calculations are carried out in full parameter space with explicit inclusion of the static bias and we compare the nature of spin density wave (SDW) and charge density wave (CDW) insulators under the influence of external electric field. We find that, although the SDW (U>2V) and CDW (U<2V) insulators enter into a conducting state after a certain threshold bias, CDW insulators require much higher bias than the SDW insulators for insulator-metal transition at zero temperature. We also find the CDW-SDW phase transition on application of external electric field. The bias required for the transitions in both cases decreases with increase in system size.Comment: 7 pages, 7 figures, accepted in J. Phys.: Condens. Matte

Gender Diversity in the Boardroom and Financial Performance of Commercial Banks: Evidence from Bangladesh

In today’s corporate world, board diversity is a much talked-about topic and gender diversity is an important aspect of board diversity. Gender diversity refers to the presence of women on corporate boards of directors. In this paper, an effort has been made to examine whether an association exists between the financial performance of commercial banks in Bangladesh and presence of women on the boards of directors of these banks and in order to examine the existence of this association, a non-parametric test, namely Kruskal-Wallis H test has been conducted. But the test has yielded conflicting results at different significance levels.Gender diversity, Board of Directors, Financial Performance and Commercial Banks

Steroid hormone regulation of fetal mouse oocyte development

The factors governing maintenance of the non-renewable reservoir of primordial follicles in female mammals remain largely elusive. During the early stages of fetal development, oocytes grow in nests or clusters known as germ cell cysts. Cysts break down into individual oocytes in the perinatal period and become enclosed by somatic pregranulosa cells to form primordial follicles. Steroid hormones have been shown by numerous studies to be one of the important factors which critically govern the process of cyst breakdown and follicle formation. There has been earlier evidence from this laboratory to indicate that exogenous exposure of neonatal mice ovaries to estradiol (E2), progesterone (P4) or E2 mimicking chemicals known as xenoestrogens such as Diethylstilbestrol (DES) and Bisphenol-A (BPA) delay cyst breakdown and follicle formation. The overall goal of this dissertation project is centered on the pivotal question: What is the source of steroid hormone signaling and its role in meiotic progression during fetal oocyte development in mice? One of the two objectives of this dissertation was to identify the sources of the steroid hormones (maternal circulation or fetal ovaries) which regulate fetal oogenesis. Our studies showed prominent expression of both mRNA and protein in the fetal ovaries for aromatase and 3-beta-hydroxysteroid dehydrogenase (3βHSD), cardinal steroidogenic enzymes required for E2 and P4 synthesis respectively. The mRNA levels for both aromatase and 3βHSD in the fetal ovaries detected by qPCR were found to decrease prior to cyst breakdown. These results align to our previous model that high levels of steroid hormones keep oocytes in cysts during fetal development and the drop in hormone levels is required to trigger cyst breakdown. To analyze the functional significance of this local steroid action, we used aromatase and 3βHSD inhibitors (letrozole and trilostane respectively) in organ culture to block hormone production by fetal ovaries. We find that the total number of oocytes was reduced in treated ovaries compared to controls. The second objective of the dissertation was to examine the relation between two temporal events in mice oogenesis: progression to the diplotene stage and primordial follicle formation. We performed a thorough quantitative analysis by nuclear morphological observations of diplotene versus prediplotene nuclei of hematoxylin and eosin stained serial sections of ovaries at different ages. Interestingly, we observed that primordial follicle formation occurs irrespective of the meiotic stage of the oocyte nuclei. Thus oocytes in follicles were found both at diplotene and pre-diplotene stages. We also wanted to understand the role of steroid hormone signaling in meiotic progression of oocytes. Our data indicate that exogenous treatment of P4 and not E2 decrease the number of follicles containing oocytes at diplotene. Such insights from the murine research models significantly contribute to our knowledge of the meiotic defects caused due to E2 or P4 exposure during fetal oogenesis in the case of human pregnancies (which often results from exposure to environmental estrogens or xenoestrogens). Aneuploidy is one of the prevalent causes for genetic disorders in humans and it arises from anomalies in the chromosome content of the gametes (sperms and ova). Any disruption in the normal meiotic events during fetal gametogenesis may be amplified along the way to give rise to aneuploid gametes. Meiotic studies in model organisms are therefore indispensable to our understanding of human aneuploidy. In summary, this dissertation project has focused on the critical role of steroid hormone regulation of fetal mouse oocyte development and its role on meiotic progression, thus contributing to our understanding of early ovarian differentiation

Comparative study of the electron conduction in azulene and naphthalene

We have studied the feasibility of electron conduction in azulene molecule and compared with that in its isomer naphthalene. We have used non-equilibrium Green's function formalism to measure the current in our systems as a response of the external electric field. Parallely we have performed the Gaussian calculations with electric field in the same bias window to observe the impact of external bias on the wave functions of the systems. We have found that, the conduction of azulene is higher than that of naphthalene inspite of its intrinsic donor-acceptor property, which leads a system to more insulating state. Due to stabilization through charge transfer the azulene system can be fabricated as a very effective molecular wire. Our calculations shows the possibility of huge device application of azulene in nano-scale instruments.Comment: 6 pages, 8 figure

Half-Metallicity in Undoped and Boron Doped Graphene Nanoribbons in Presence of Semi-local Exchange-Correlation Interactions

We perform density functional calculations on one-dimensional zigzag edge graphene nano-ribbons (ZGNRs) of different widths, with and without edge doping including semi-local exchange-correlations. Our study reveals that, although the ground state of edge passivated (with hydrogen) ZGNRs prefers to be anti-ferromagnetic, the doping of both the edges with Boron atoms stabilizes the system in a ferromagnetic ground state. Both the local and semi-local exchange-correlations result in half-metallicity in edge passivated ZGNRs at a finite cross-ribbon electric field. However, the ZGNR with Boron edges shows half-metallic behavior irrespective of the ribbon-width even in absence of electric field and this property sustains for any field strength, opening a huge possibility of applications in spintronics.Comment: 13 pages, 4 figure