Effect of disorder on the electronic properties of graphene: a theoretical approach

In order to manipulate the properties of graphene, its very important to understand the electronic structure in presence of disorder. We investigate, within a tight-binding description, the effects of disorder in the on-site (diagonal disorder) term in the Hamiltonian as well as in the hopping integral (off-diagonal disorder) on the electronic dispersion and density of states by augmented space recursion method. Extrinsic off-diagonal disorder is shown to have dramatic effects on the two-dimensional Dirac-cone, including asymmetries in the band structures as well as the presence of discontinuous bands in certain limits. Disorder-induced broadening, related to the scattering length (or life-time) of electrons, is modified significantly with the increasing strength of disorder. We propose that our theory is suitable to study the effects of disorder in other 2D materials, e.g., a boron nitride monolayer.Comment: 11 pages, 8 figure

Attitudes of Islamic Learning and Education Faculty Students Towards English Language at Karachi University

The research paper aims at studying the attitudes of the students of Islamic Learning and Education Faculty towards English at the University of Karachi. It is based on testing the hypothesis that the students of Islamic Learning Faculty have less positive attitudes towards English as compared to the students of Education faculty through a survey on first year students of both faculties. A five-point Likert scale was used to conduct a survey on 151 students of the Islamic Learning faculty and 135 students of the Education faculty. The results were calculated using an independent t-testand standard deviation which reveals that there is a minor difference in the attitudes of thestudent of both faculties. The students of the Education faculty showed more positive attitudes when asked about the importance of English as compared to the attitudes of the students of Islamic Learning Faculty. However, the difference in their attitude is negligible. As the results reveal a minor association between the attitudes of the learners and their faculty, the study; therefore, proves the null hypothesiswhich says that there is no significant difference between the attitudes of the students of both the faculties. Keywords: attitudes; English language; t-test; standard deviation; Islamic learning faculty; education faculty; likert-scale

Lattice thermal conductivity of disordered NiPd and NiPt alloys

Numerical calculations of lattice thermal conductivity are reported for the binary alloys NiPd and NiPt. The present work is a continuation of an earlier paper by us [PRB, 72, 214207 (2005)]which had developed a theoretical framework for the calculation of configuration-averaged lattice thermal conductivity and thermal diffusivity in disordered alloys. The formulation was based on the augmented space theorem combined with a scattering diagram technique. In this paper we shall show dependence of the lattice thermal conductivity on a series of variables like phonon frequency, temperature and alloy composition. The temperature dependence of $\kappa(T)$ and its realtion to the measured thermal conductivity is discussed. The concentration dependence of $\kappa$ appears to justify the notion of a minimum thermal conductivity as discussed by Kittel, Slack and others. We also study the frequency and composition dependence of the thermal diffusivity averaged over modes. A numerical estimate of this quantity gives an idea about the location of mobility edge and the fraction of states in the frequency spectrum which is delocalized.Comment: 23 pages, 18 figure

Structural modeling of natural citrus products as potential cross-strain inhibitors of Dengue virus

There are four serotypes of Dengue virus and there are existing drugs used against specific serotype. There is no drug that is effective against all strains of this virus. In this research, bioinformatics tools were used to predict the affinity of natural ligands for the glycoprotein E of Dengue virus by considering the conserved domains. Molecular docking studies were carried out by using Autodock 3.0. Computational analysis which showed that two ligands have the potential to inhibit the site in glycoprotein E and control of all strains is now possible by these ligands.Key words: Bioinformatics, multivariate drug designing, Dengue virus, in silico drug for dengue, glycoprotein E, conserved domain

Soil-Pile Interaction Parameters in Vertical and Torsional Vibrations

In this paper, two lumped parameter analogues with the inclusion of constant friction damping are suggested to explain the dynamic behavior of pile supported footings during vertical as well as torsional modes of vibrations. Simple theoretical procedures have been described by which the constant frictional force and the constant frictional moment of the friction damping can be evaluated during vertical and torsional vibrations respectively. The suggested procedures into consideration the relevant physical characteristics of the interface between the pile and the soil, as also the length to diameter (L/d) ratio of the pile. Field vibratory teats have been carried out on model pile supported footings under steady state vertical and torsional excitation. The test data obtained are compared with the values predicted by the proposed theory and the agreement between the two is found to be satisfactory

Lead-free Magnetic Double Perovskites for Photovoltaic and Photocatalysis Applications

The magnetic spin degrees of freedom in magnetic materials serve as additional capability to tune materials properties, thereby invoking magneto-optical response. Herein, we report the magneto-optoelectronic properties of a family of lead-free magnetic double perovskites Cs_{2}AgTX_{6} (T = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu; X=Cl, Br, I). This turns out to provide an extremely fertile series, giving rise to potential candidate materials for photovoltaic(PV) applications. In conjunction with high absorption coefficient and high simulated power conversion efficiency for PV applications, few compounds in this series exhibit novel magnetic character useful for spintronic applications. The interaction between magnetism and light can have far-reaching results on the photovoltaic properties as a consequence of the shift in the defect energy levels due to Zeeman effect. This subsequently affects the recombination rate of minority carriers, and hence the photoconversion efficiency. Moreover, the distinct ferromagnetic and anti-ferromagnetic ordering driven by hybridization and super-exchange mechanism can play a significant role to break the time-reversal and/or inversion symmetry. Such a coalescence of magnetism and efficient optoelectronic response has the potential to trigger magnetic/spin anomalous photovoltaic (non-linear Optical) effect in this Cs$_{2}$AgTX$_{6}$ family. These insights can thus channelize the advancement of lead-free double perovskites in magnetic/spin anomalous photovoltaic field as well.Comment: 9 pages, 5 figures, 1 tabl