Synchronous and Asynchronous Mott Transitions in Topological Insulator Ribbons

We address how the nature of linearly dispersing edge states of two dimensional (2D) topological insulators evolves with increasing electron-electron correlation engendered by a Hubbard like on-site repulsion $U$ in finite ribbons of two models of topological band insulators. Using an inhomogeneous cluster slave rotor mean-field method developed here, we show that electronic correlations drive the topologically nontrivial phase into a Mott insulating phase via two different routes. In a synchronous transition, the entire ribbon attains a Mott insulating state at one critical $U$ that depends weakly on the width of the ribbon. In the second, asynchronous route, Mott localization first occurs on the edge layers at a smaller critical value of electronic interaction which then propagates into the bulk as $U$ is further increased until all layers of the ribbon become Mott localized. We show that the kind of Mott transition that takes place is determined by certain properties of the linearly dispersing edge states which characterize the topological resilience to Mott localization.Comment: 4+ pages, 5 figure

Twelfth Grade Kuwaiti Students’ Identification of Domain and Range in Graphical Representation of Function and the Meaning they Ascribe to them

This research investigated twelfth grade students' performance in identification of domain and range of functions in a graphical representation. The study focused on four types of functions: polynomial, trigonometry, piecewise and discontinuous. The study also aimed to identify the meaning that students gave for the domain and range and how they identified them. To collect the data two instruments were used: a test and an interview. A sample of 216 students participated in the study. The results showed a low performance in identifying domain and range for functions in graphical representation. The T-test indicated a statistical difference in students’ performance in domain and range in favor of domain. The results indicated a statistically significant difference in students' performance among the different types of function. Tukey test showed that the difference was in favor of polynomial against the other types of function. Also there was a significant difference between trigonometry and piecewise items in favor of trigonometry. The interviews revealed that students’ meaning and common practices in identifying the domain and range reflected misunderstandings. Some of them highlighted that the domain is the x-axis and y-axis or the x-intercept and y- intercept. Others considered that the curve as the domain or the range

Induced polarization and electronic properties of carbon doped boron-nitride nanoribbons

The electronic properties of boron-nitride nanoribbons (BNNRs) doped with a line of carbon atoms are investigated by using density functional calculations. Three different configurations are possible: the carbon atoms may replace a line of boron or nitrogen atoms or a line of alternating B and N atoms which results in very different electronic properties. We found that: i) the NCB arrangement is strongly polarized with a large dipole moment having an unexpected direction, ii) the BCB and NCN arrangement are non-polar with zero dipole moment, iii) the doping by a carbon line reduces the band gap independent of the local arrangement of boron and nitrogen around the carbon line, iv) an electric field parallel to the carbon line polarizes the BN sheet and is found to be sensitive to the presence of carbon dopants, and v) the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital decreases linearly with increasing applied electric field directed parallel to the carbon line. We show that the polarization and energy gap of carbon doped BNNRs can be tuned by an electric field applied parallel along the carbon line.Comment: 11 pages, 6 figure

Leptin and systemic lupus erythematosus: A comprehensive review

Leptin, a cytokine-like hormone produced by adipocytes, modulates innate and adaptive responses of the immune system. Several reports have indicated that leptin exerts pro-inflammatory effects which significantly trigger autoimmune responses in chronic inflammatory diseases e.g. systemic lupus erythematosus (SLE), an inflammatory, multi-system disease characterized by the presence of autoantibodies. Irrespective of contradictory results, many studies have indicated that leptin concentrations are increased in SLE patients. This might reflect genetic association, or a mechanism underlying the pathogenesis of SLE. To shed light on this possibility, recent studies investigated several polymorphism genes related to leptin in SLE patients from different ancestral groups. This review focuses on current understanding of the role of leptin in the pathogenesis of SLE and its immunomodulatory effects. This is expected to provide new leptin-based therapeutic interventions as modern approaches which are safer than the currently used ones for the treatment of SLE. Keywords: Leptin, Systemic Lupus Erythematosus, Polymorphism, Gene expressio

Wet granulation to overcome liquisolid technique issues of poor flowability and compactibility: A study to enhance Glibenclamide dissolution

The aim of this study is to apply wet granulation on liquisolid powders to overcome issues of poor powder flowability and compressibility especially with using high viscosity liquid vehicles. Different liquisolid formulations were made using three excipients where the effect of each excipient used in the dissolution of the model hydrophobic drug (Glibenclamide) was evaluated. The Glibenclamide tablets were formulated using PEG 400, Synperonic PE/L44 and Cremophor ELP, at a 10 %w/w in liquid vehicle drug concentration. The carrier (Avicel®PH102) was used followed by colloidal silicon dioxide (coating material) that converted the wet mixture into dry powder. Potato starch, 5%w/w, as a disintegrant was mixed with the mixture manually for 10 minutes and was finalized by adding 0.75% of magnesium stearate as a lubricant. The final powder (depending on its flowability and compactability) was then compacted automatically using a single-punch tableting machine to give tablets with 4mg unit drug dose. Prepared liquisolid compacts were characterised via B.P. quality control tests. In this study, a novel discovery was achieved to overcome the major problems with liquisolid preparations (flowability and compactability). This new technique is the wet granulation process to be applied with liquisolid powders just before the compaction stage of the powders into tablets. Consequently, it was found that by application of wet granulation to liquisolid powder admixture, the large-scale production of liquisolid compacts is feasible and can be easily applied by pharmaceutical industry. As with some liquisolid vehicles especially high viscosity although very good to enhance dissolution usually formulations are studied in powder forms [1,2]

Effect of Aqueous and Ethanolic Extracts of Tribulus terrestris, Phoenix dactylifera and Nasturtium officinale Mixture on Some Reproductive Parameters in Male Mice

The present investigation was conducted to evaluate the effect of the crude extracts mixture of three plants (Tribulus terrestris, Phoenix dactylifera and Nasturtium officinale) on semen quality,sex hormones and reproductive performance of mature male mice. A group of 25 male mice given 150mg/kg/day of the powder of the plants mixture with the food for four weeks and another three groups of 25 animals each given intraperitoneal injection from each of the aqueous and ethanolic extracts with a doses 75, 150, and 300mg/kg/day for two weeks. A remarkable increase in sperm concentration and motility with a decreased abnormal morphology was obtained in the experimental groups. A significant increase in hormones level were recognized in most groups. The results of mating untreated females with treated males of the four experimental groups revealed a decreased gestation period and an increased litter size. The results showed a dose dependent pattern of activity and the effect of the extracts were enhanced with increasing the dose level. The ethanolic extract being the more effective extract in all parameters

Electronic, dielectric and optical properties of two dimensional and bulk ice: a multi-scale simulation study

The intercalated water into nanopores exhibits anomalous properties such as ultralow dielectric constant.~Multi-scale modeling and simulations are used to investigate the dielectric properties of various crystalline two-dimensional ices and bulk ices. Although, the structural properties of two-dimensional (2D-) ices have been extensively studied, much less is known about their electronic and optical properties. First, by using density functional theory (DFT) and density functional perturbation theory (DFPT), we calculate the key electronic, optical and dielectric properties of 2D-ices. Performing DFPT calculations, both the ionic and electronic contributions of the dielectric constant are computed. The in-plane electronic dielectric constant is found to be larger than the out-of-plane dielectric constant for all the studied 2D-ices. The in-plane dielectric constant of the electronic response is found to be isotropic for all the studied ices. Secondly, we determined the dipolar dielectric constant of 2D-ices using molecular dynamics simulations (MDS) at finite temperature. The total out-of-plane dielectric constant is found to be larger than 2 for all the studied 2D-ices. Within the framework of the random-phase approximation (RPA), the absorption energy ranges for 2D-ices are found to be in the ultraviolet spectra. For the comparison purposes, we also elucidate the electronic, dielectric and optical properties of four crystalline ices (ice VIII, ice XI, ice Ic and ice Ih) and bulk water

Spiral graphone and one sided fluorographene nano-ribbons

The instability of a free-standing one sided hydrogenated/fluorinated graphene nano-ribbon, i.e. graphone/fluorographene, is studied using ab-initio, semiempirical and large scale molecular dynamics simulations. Free standing semi-infinite arm-chair like hydrogenated/fluorinated graphene (AC-GO/AC-GF) and boat like hydrogenated/fluorinated graphene (B-GO/B-GF) (nano-ribbons which are periodic along the zig-zag direction) are unstable and spontaneously transform into spiral structures. We find that rolled, spiral B-GO and B-GF are energetically more favorable than spiral AC-GO and AC-GF which is opposite to the double sided flat hydrogenated/fluorinated graphene, i.e. graphane/fluorographene. We found that the packed, spiral structures exhibit unexpected localized HOMO-LUMO at the edges with increasing energy gap during rolling. These rolled hydrocarbon structures are stable beyond room temperature up to at least $T$=1000\,K.Comment: Phys. Rev. B 87, 075448 (2013