Tunable Band Gap in Graphene with a Non-Centrosymmetric Superlattice Potential

We show that, if graphene is subjected to the potential from an external superlattice, a band gap develops at the Dirac point provided the superlattice potential has broken inversion symmetry. As a numerical example, we calculate the band structure of graphene in the presence of an external potential due to periodically patterned gates arranged in a triangular graphene superlattice (TGS) with broken inversion symmetry, and find that a band gap is created at both the original and "second generation" Dirac point. The gap can be controlled, in principle, by changing the external potential and the lattice constant of the TGS.Comment: 6 figures, Phys. Rev. B 79, 20543

Switchable valley filter based on a graphene pp-nn junction in a magnetic field

Low-energy excitations in graphene exhibit relativistic properties due to the linear dispersion relation close to the Dirac points in the first Brillouin zone. Two of the Dirac points located at opposite corners of the first Brillouin zone can be chosen as inequivalent, representing a new valley degree of freedom, in addition to the charge and spin of an electron. Using the valley degree of freedom to encode information has attracted significant interest, both theoretically and experimentally, and gave rise to the field of valleytronics. We study a graphene $p$-$n$ junction in a uniform out-of-plane magnetic field as a platform to generate and controllably manipulate the valley polarization of electrons. We show that by tuning the external potential giving rise to the $p$-$n$ junction we can switch the current from one valley polarization to the other. We also consider the effect of different types of edge terminations and present a setup, where we can partition an incoming valley-unpolarized current into two branches of valley-polarized currents. The branching ratio can be chosen by changing the location of the $p$-$n$ junction using a gate.Comment: 8 pages, 7 figure

Numerical method for evolving the Projected Gross-Pitaevskii equation

In this paper we describe a method for evolving the projected Gross-Pitaevskii equation (PGPE) for a Bose gas in a harmonic oscillator potential. The central difficulty in solving this equation is the requirement that the classical field is restricted to a small set of prescribed modes that constitute the low energy classical region of the system. We present a scheme, using a Hermite-polynomial based spectral representation, that precisely implements this mode restriction and allows an efficient and accurate solution of the PGPE. We show equilibrium and non-equilibrium results from the application of the PGPE to an anisotropic trapped three-dimensional Bose gas.Comment: 12 pages, 5 figures. To appear in Phys. Rev. E. Convergence results added, a few minor changes made and typos fixe

Kozmološki model s promjenljivim G i Λ članom u općoj relativnosti

Einstein\u27s field equations with variable gravitational constant and cosmological constants are considered in the presence of perfect fluid for Bianchi type-I universe by assuming the cosmological term proportional to R−m (R is scale factor and m is a constant). The model approaches quasi-isotropic state. The cosmological term decreases with increasing time. We obtain that the present universe is accelerating with a large fraction of cosmological density in the from of cosmological term.Proučavamo Einsteinove jednadžbe polja s promjenljivom gravitacijskom konstantom i kozmološkim konstantama u prisustvu perfektne tekućine za Bianchijev svemir tipa I pretpostavljajući kozmološki član razmjeran R−m (R je faktor sumjeravanja a m stalnica). Model teži kvaziizotropnom stanju. Kozmološki član pada s porastom vremena. Dobivamo da se sadašnji svemir ubrzava s velikim udjelom kozmološke gustoće u vidu kozmološkog člana

Model za objašnjenje promjenljivih G i Λ uz stalan parametar usporavanja

We study the evolution of homogeneous and anisotropic Bianchi type-I cosmological models in the presence of perfect fluid with variable G and L by assuming a special law of variation for Hubble\u27s parameter that yields a constant value of the deceleration parameter. Some physical consequences of the model are discussed in the case of Zel\u27dovich fluid and radiation-dominated fluid.Proučavamo razvoj za homogene i anizotropne Bianchijeve kozmološke modele tipa I u prisustvu perfektne tekućine s promjenljivim G i Λ, pretpostavljajući posebnu ovisnost Hubbleovog parametra koja daje stalnu vrijednost parametra usporavanja. Raspravljaju se neki fizički ishodi modela za slučaj Zel’dovicheve tekućine i tekućinu u kojoj prevladava zračenje

Model za objašnjenje promjenljivih G i Λ uz stalan parametar usporavanja

We study the evolution of homogeneous and anisotropic Bianchi type-I cosmological models in the presence of perfect fluid with variable G and L by assuming a special law of variation for Hubble\u27s parameter that yields a constant value of the deceleration parameter. Some physical consequences of the model are discussed in the case of Zel\u27dovich fluid and radiation-dominated fluid.Proučavamo razvoj za homogene i anizotropne Bianchijeve kozmološke modele tipa I u prisustvu perfektne tekućine s promjenljivim G i Λ, pretpostavljajući posebnu ovisnost Hubbleovog parametra koja daje stalnu vrijednost parametra usporavanja. Raspravljaju se neki fizički ishodi modela za slučaj Zel’dovicheve tekućine i tekućinu u kojoj prevladava zračenje

Kozmološki model s promjenljivim G i Λ članom u općoj relativnosti

Einstein\u27s field equations with variable gravitational constant and cosmological constants are considered in the presence of perfect fluid for Bianchi type-I universe by assuming the cosmological term proportional to R−m (R is scale factor and m is a constant). The model approaches quasi-isotropic state. The cosmological term decreases with increasing time. We obtain that the present universe is accelerating with a large fraction of cosmological density in the from of cosmological term.Proučavamo Einsteinove jednadžbe polja s promjenljivom gravitacijskom konstantom i kozmološkim konstantama u prisustvu perfektne tekućine za Bianchijev svemir tipa I pretpostavljajući kozmološki član razmjeran R−m (R je faktor sumjeravanja a m stalnica). Model teži kvaziizotropnom stanju. Kozmološki član pada s porastom vremena. Dobivamo da se sadašnji svemir ubrzava s velikim udjelom kozmološke gustoće u vidu kozmološkog člana

Mercury or Mercury Free Restorations in Oral Cavity

Amalgam is basically a concoction of metals that has been used as a potent filling material in dentistry for the last 150 years. Amalgam usually consists of silver, mercury, tin and copper. Dental amalgam is a material used to fill cavities of tooth. Over the years, amalgam has become a topic of concern because it contains mercury. Mercury is a naturally occurring metal in the environment. Mercury exists as a liquid in room temperature but when heated, it becomes a gas. Flexibility of amalgam as a filling material is due Mercury. An alloy powder, a compound that is soft in nature when mixed with mercury makes it enough to mix and condense into the tooth. It hardens quickly and offers strong resistance to the forces of biting and chewing. There are studies reported on the safety of amalgam fillings. In 2005, European Union launched a comprehensive mercury strategy to reduce use of mercury. In 2008, countries like Norway and Denmark restricted the use of dental amalgam containing mercury. In 2009, this research was evaluated by U.S. Food and Drug Administration (FDA) and found no rationale to limit the use of amalgam. There are certain restorative materials that are available commercially that are mercury free in nature like Gold, Porcelain, Gallium alloys, Composite resin restoratives etc. They offer many advantages over amalgams containing mercury like: seals the dentin from future decay, reinforces remaining tooth structure, provides smooth and bonded margins, conservative and it blends naturally