Algorithm for determining the concentrations of substances from spectral data without using standard samples of known composition

Some questions in the general theory of the spectral determination of the composition of mixtures of substances are discussed. Results from a large series of computer simulations are presented which demonstrate the possibility of quantitative analysis of mixtures of substances using a set of spectral measurements and the statistics of the computed spectra. It is found that, in general, the results of an analysis can be described by a matrix whose elements reflect the errors in both the experiments and the calculations.     

Application of the differential method for determining the composition of a toluene-methyl ethyl ketone mixture by an IR analyzer

A differential method is suggested to analyze two-component systems. It allows a 1.5-fold increase in sensitivity as compared to the ordinary procedure for determination of the composition of toluene-methyl ethyl ketone by an 1R continuous-flow analyzer. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 3, pp. 408–409, May–June, 1999.     

Bipolaron formation in the presence of magnetic impurities

The formation of bipolarons in the presence of magnetic impurities is studied theoretically. We use the extended Hubbard Su–Schrieffer–Heeger (SSH) model with Brazovskii–Kirova and Kondo interaction terms. Parameters are chosen suitably for cis-polyacetylene. A Quantum Monte Carlo (QMC) algorithm is used to study the equilibrium lattice structure and charge distribution as a function of doping level and Kondo exchange integral. The magnetic impurities can have a destructive effect on bipolaron stability, instead favouring the two polaron configuration. However by suitably adjusting the doping level, bipolarons can be stabilized over a wide range of impurity strength.     

Kondo effect in the presence of magnetic impurities

We measure transport through gold grain quantum dots fabricated using electromigration, with magnetic impurities in the leads. A Kondo interaction is observed between dot and leads, but the presence of magnetic impurities results in a gate-dependent zero-bias conductance peak that is split due to a RKKY interaction between the spin of the dot and the static spins of the impurities. A magnetic field restores the single Kondo peak in the case of an antiferromagnetic RKKY interaction. This system provides a new platform to study Kondo and RKKY interactions in metals at the level of a single spin.     

Hall Conductivity in the presence of repulsive magnetic impurities

The Hall conductivity of disordered magnetic systems consisting of hard-core point vortices randomly dropped on the plane with a Poissonian distribution, has a behavior analogous to the one observed experimentally by Haug, Gerhardts, Klitzling and Ploog, with repulsive scatterers [#!1!#]. We also argue that models of homogeneous magnetic field with disordered potential, have necessarily vanishing Hall conductivities when their Hilbert space is restricted to a given Landau level subspace. Received: 29 September 1998 / Accepted: 21 December 1998     

Electron energy relaxation in the presence of magnetic impurities

We study inelastic electron-electron scattering mediated by the exchange interaction of electrons with magnetic impurities and find the kernel of the corresponding two-particle collision integral. In a wide region of parameters, the kernel K is proportional to the inverse square of the transferred energy, K proportional to J4/E2. The exchange constant J is renormalized due to the Kondo effect. At small energy transfers, the 1/E2 divergence is cut off; the cutoff energy is determined by the dynamics of the impurity spins. The obtained results may provide a quantitative explanation of the experiments of Pothier et al. [Phys. Rev. Lett. 79, 3490 (1997)] on anomalously strong energy relaxation in short metallic wires.     

Group-theoretic method for determining the number of superlattices in alloys of a given composition

The influence of the crystallographic symmetry of the lattice of an alloy on the various configurations of occupation of the sublattices by different species of atoms is investigated with regard for the concentrations of the latter. Two occupation configurations are considered to be equivalent if one can be reduced to the other by a transformation from the Fedorov lattice group. The equivalence classes of occupation configurations correspond to superlattices in the alloy. The machinery of the theory of group representations and the theory of invariants is used to determine the number of superlattices and their geometry.     

Two-dimensional electrons in the presence of spin-orbit scattering by impurities

A two-dimensional disordered system of interacting electrons when the principal source of spin relaxation is the spin-orbit scattering by impurities, is studied. It is shown that in this system conductivity has a very complicated behaviour since there is a focus on the phase plane of the renormalization group equations.     

Density of states in the presence of a strong magnetic field and random impurities

A supersymmetric formalism is used to rederive a recent beautiful result of Wegner concerning the density of state of an electron gas in the presence of a strong magnetic field and impurities. The derivation is simple and applicable to any (local) distribution of scatterers. Explicit formulae are given in two dimensions. A Poisson distribution of scatterers leads to an interesting condensation phenomenon when the magnetic field is increased.     

Electron-level dynamics in the presence of impurities and the Ruijsenaars-Schneider model

The dynamic equations for the energy level of a finite system with impurities are shown to be equivalent to the rational Ruijsenaars-Schneider system. The action, which is simultaneously the generating function of the Bäcklund canonical transformation for this system, is calculated. Various variants of statistical averaging of the energy-level distribution are discussed.     

Correlations in the director-orientation fluctuations in the presence of microscopic impurities in a nematic liquid crystal

The model of a spatially restricted liquid-crystal system with microscopic impurities homogeneously distributed in the system is considered. The thermodynamic correlations of the director-orientation fluctuations and the correlations of the scalar order parameter characterizing impurities in the system are investigated for this system. It is shown that the impurity correlations are weaker than in a pure isotropic liquid. The correlations in the director deviations depend essentially on the wavevector and can be substantially weakened in the presence of impurities.     

Growth of tellurium clusters in presence of metal impurities

The growth of small tellurium clusters in helium and the influence of a metal impurity (dysprosium atoms) on the cluster size distribution are investigated in a double laser vaporization source. A model describing the role of the carrier gas as collision partner is presented, emphasizing the crucial influence of the gas pressure on cluster formation. Changes in cluster reactivity due to dysprosium addition are discussed in terms of ionic structures Dy ^{3 +}(Te _N)^{3 -} containing a radical electron. Received 28 November 2000     

Ground state of graphene in the presence of random charged impurities

We calculate the carrier-density-dependent ground-state properties of graphene in the presence of random charged impurities in the substrate taking into account disorder and interaction effects nonperturbatively on an equal footing in a self-consistent theoretical formalism. We provide detailed quantitative results on the dependence of the disorder-induced spatially inhomogeneous two-dimensional carrier density distribution on the external gate bias, the impurity density, and the impurity location. We find that the interplay between disorder and interaction is strong, particularly at lower impurity densities. We show that, for the currently available typical graphene samples, inhomogeneity dominates graphene physics at low (< or approximately 10(12) cm(-2)) carrier density with the density fluctuations becoming larger than the average density.     

Bound states in disclinated graphene with Coulomb impurities in the presence of a uniform magnetic field

In this contribution, we study the effects caused by an impurity on the quantum dynamics of massive excitations in a disclinated graphene in the presence of an external magnetic field. Within a continuum approach, the problem is mathematically modeled by the definition of a special vector potential containing all the information about the topology and the interacting fields. The presence of disclination is introduced by a term in the Dirac equation that translates the appearance of a phase associated with the transport of the spinor around the apex of the cone. We solve exactly the Dirac equation for this problem and the eigenvalues are obtained. We observe the influence of the disclination on the spectrum of energy and the allowed values of magnetic field.