Cumulene Molecular Wire Conductance from First Principles

We present first principles calculations of current-voltage characteristics (IVC) and conductance of Au(111):S2-cumulene-S2:Au(111) molecular wire junctions with realistic contacts. The transport properties are calculated using full self-consistent ab initio NEGF-DFT methods under external bias. The conductance of the cumulene wires shows oscillatory behavior depending on the number of carbon atoms (double bonds). Among all conjugated oligomers, we find that cumulene wires with odd number of carbon atoms yield the highest conductance with metallic-like ballistic transport behavior. The reason is the high density of states in broad LUMO levels spanning the Fermi level of the electrodes. The transmission spectrum and the conductance depend only weakly on applied bias, and the IVC is nearly linear over a bias region from +1 to -1 V. Cumulene wires are therefore potential candidates for metallic connections in nanoelectronic applications.Comment: Accepted in Phys. Rev. B; 5 pages and 6 figure

Limitations of Algebraic Approaches to Graph Isomorphism Testing

We investigate the power of graph isomorphism algorithms based on algebraic reasoning techniques like Gr\"obner basis computation. The idea of these algorithms is to encode two graphs into a system of equations that are satisfiable if and only if if the graphs are isomorphic, and then to (try to) decide satisfiability of the system using, for example, the Gr\"obner basis algorithm. In some cases this can be done in polynomial time, in particular, if the equations admit a bounded degree refutation in an algebraic proof systems such as Nullstellensatz or polynomial calculus. We prove linear lower bounds on the polynomial calculus degree over all fields of characteristic different from 2 and also linear lower bounds for the degree of Positivstellensatz calculus derivations. We compare this approach to recently studied linear and semidefinite programming approaches to isomorphism testing, which are known to be related to the combinatorial Weisfeiler-Lehman algorithm. We exactly characterise the power of the Weisfeiler-Lehman algorithm in terms of an algebraic proof system that lies between degree-k Nullstellensatz and degree-k polynomial calculus

Quantum treatment of neutrino in background matter

Motivated by the need of elaboration of the quantum theory of the spin light of neutrino in matter ($SL\nu$), we have studied in more detail the exact solutions of the Dirac equation for neutrinos moving in the background matter. These exact neutrino wavefunctions form a basis for a rather powerful method of investigation of different neutrino processes in matter, which is similar to the Furry representation of quantum electrodynamics in external fields. Within this method we also derive the corresponding Dirac equation for an electron moving in matter and consider the electromagnetic radiation ("spin light of electron in matter", $SLe$) that can be emitted by the electron in this case.Comment: 10 pages, in: Proceedings of QFEXT'05 (The Seventh Workshop on Quantum Field Theory under the Influence of External Conditions, IEEC, CSIC and University of Barcelona, Barcelona, Catalonia, Spain, 5-9 September 2005.), ed. by Emilio Elizalde and Sergei Odintsov; published in Journal of Physics

The HVEDC Method for the Production of Tungsten Based Alloys

The purpose of this study is to investigate HVEDC method for the production of tungsten-based alloys. It is established that the method of high-voltage electro-discharge compaction, in addition to some economic and time benefits, contributes to a minimal change in the microstructure and does not lead to grain growth, therebyimproving mechanical characteristics. Keywords: powder metallurgy, tungsten heavy alloys, high-voltage electro-discharge consolidation

Liquid drop in a cone - line tension effects

The shape of a liquid drop placed in a cone is analyzed macroscopically. Depending on the values of the cone opening angle, the Young angle and the line tension four different interfacial configurations may be realized. The phase diagram in these variables is constructed and discussed; it contains both the first- and the second-order transition lines. In particular, the tricritical point is found and the value of the critical exponent characterizing the behaviour of the system along the line of the first-order transitions in the neighbourhood of this point is determined.Comment: 11 pages, 4 figure

A functional description of the model for the protection of the environmental interests of the Russian Federation in the Baltic Sea region

This article identifies the objective conditions of the conflict between the interests of development and those of environmental security. The latter are given added urgency when, within the same ecological unit, one country needs to develop and another to protect its environmental interests. The borders of the countries and regions, the economies of which affect the safety of Russia’s interests in the Baltic, do not coincide with the boundaries of the ecosystems. This calls for a study of the legal protection of Russia’s environmental interests in the Baltic Sea region. There is no legal mechanism for ensuring a balance between the interests of development and those of environmental security of the countries that have shorelines along the Baltic Sea. Thus, it is necessary to give a functional description of the regional model for the legal protection of the environmental interests of the Russian Federation in the Baltic region. To this end, we identify the juridical content of the environmental interests of the Russian Federation. We consider the possibilities of the legal protection of the environmental interests in the national and international jurisdiction. The interests are divided into two groups respectively. We reveal the essence of the environmental interests of the Russian Federation in the Baltic Sea region. We analyse the case of the Russian regions located within the Baltic Sea catchment area to test an approach to identifying the region’s boundaries. This approach may be used in modelling the regional level of the legal protection of Russia’s environmental interests in the Baltic region. We identify the environmental interests of the Russian Federation in the Baltic Sea region, as well as the forms of legal protection of the country’s interests in this territory. We describe the elements of the system of the legal protection of Russia’s interests in the Baltic region and examine the functions of these elements. The result of this study is a functional description of the model of legal protection of the environmental interests of the Russian Federation in the Baltic region. This model may be used to strengthen the links between the elements of the protection of the legitimate interests of the Russian Federation in the Baltic region

Transport of Dirac quasiparticles in graphene: Hall and optical conductivities

The analytical expressions for both diagonal and off-diagonal ac and dc conductivities of graphene placed in an external magnetic field are derived. These conductivities exhibit rather unusual behavior as functions of frequency, chemical potential and applied field which is caused by the fact that the quasiparticle excitations in graphene are Dirac-like. One of the most striking effects observed in graphene is the odd integer quantum Hall effect. We argue that it is caused by the anomalous properties of the Dirac quasiparticles from the lowest Landau level. Other quantities such as Hall angle and Nernst signal also exhibit rather unusual behavior, in particular when there is an excitonic gap in the spectrum of the Dirac quasiparticle excitations.Comment: 25 pages, RevTeX4, 8 EPS figures; final version published in PR