On local and global currents in mesoscopic conductors

Using linear response theory we show that, in a quasi-stationary state, the local multiprobe conductance of a mesoscopic system of non-interacting electrons with a time reversal invariant Hamiltonian does not depend on the local shape of the driving self-consistent potential and thus is entirely determined by the asymptotic values of the potential in the leads. In the ballistic limit, the local conductance in the lateral direction exhibits oscillations depending on the occupation of channels. Scattering by a point impurity leads to softening of the quantized global conductance steps. In addition to that for an attractive scattering potential, a dip occurs in each plateau regime the shape of which is calculated for different values of the potential strength. We also investigate the local conductance for both a point scatterer and a finite scattering region.     

Structure of the species formed from molybdenum naphthenate in the reaction with 1-phenylethyl hydroperoxide

IR and elemental analysis data indicate that the probable structure of the title compound is MoOL₂ORH or MoOL₂OORH which is formed directly from the radical within the coordination sphere of the catalyst (L=ligand).

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- , , , MoOL₂ORH MoOL₂OORH. (L=).

     

Nanoparticles prepared by self-assembly of Chitosan and poly-γ-glutamic acid

The present paper describes the preparation and characterization of novel biodegradable nanoparticles based on self-assembly of poly-gamma-glutamic acid (γ-PGA) and chitosan (CH). The nanosystems were stable in aqueous media at low pH conditions. Solubility of the systems was determined by turbidity measurements. Surface charge and mobility were measured electrophoretically. The particle size and the size distribution of the polyelectrolyte complexes were identified by dynamic light scattering and transmission electron microscopy (TEM). It was found that the size and size distribution of the nanosystems depends on the concentrations of γ-PGA and CH solutions and their ratio as well as on the pH of the mixture and the order of addition. The diameter of individual particles was in the range of 20–285 nm measured by TEM, and the average hydrodynamic diameters were between 150 and 330 nm. These biodegradable, self-assembling stable nanocomplexes might be useful for several biomedical applications.     

Note on the Wiedemann-Franz law and the Mott rule in two-dimensional systems in strong magnetic fields

Modivated by a contradiction in the literature, the range of validity of the Wiedemann-Franz law and the Mott rule has been reexamined for a 2d electron-impurity system in a strong magnetic field. The condition for these laws to be fulfilled is shown to be thermal energy level broadening rather than thermal energycyclotron energy.Dedicated to B. Mühlschlegel on the occasion of his 60th birthday     

Size distribution of nanoparticle aggregates in an aqueous magnetic fluid based on atomic-force microscopy data

Atomic-force microscopy (AFM) has been applied in a fluid environment to determine the size distribution function of nanoparticle aggregates in an aqueous magnetic fluid with magnetite particles coated by polyacrylic acid for stabilization. It is proposed to use an external magnetic field to anchor aggregates on the substrate. The data are compared with the AFM data for dried precipitates of the system under consideration, formed during evaporation of the liquid carrier under different conditions, as well as with the particle size distribution in the initial system obtained from small-angle X-ray scattering data.     

Sulfated meroterpenoids from the Brazilian sponge Callyspongia sp. are inhibitors of the antileishmaniasis target adenosine phosphoribosyl transferase

Three new disulfated meroterpenoids, ilhabelanol (1), ilhabrene (2), and isoakaterpin (3), have been isolated from extracts of the Brazilian marine sponge Callyspongia sp. Isoakaterpin (3) inhibits Leishmania spp. adenosine phosphoribosyl transferase with an IC50 of 1.05 microM. The structures of 1, 2, and 3 were elucidated by analysis of one- and two-dimensional NMR data. Ilhabelanol (1) and ilhabrene (2) both have unprecedented meroterpenoid carbon skeletons.     

Irreducibility criteria of Schur-type and Pólya-type

Let f(x)=(x-a₁)?(x-a_m){f(x)=(x-a_1)\cdots (x-a_m)}, where a ₁, . . . , a _m are distinct rational integers. In 1908 Schur raised the question whether f(x) ± 1 is irreducible over the rationals. One year later he asked whether (f(x))^2k+1{(f(x))^{2^k}+1} is irreducible for every k ≥ 1. In 1919 Pólya proved that if P(x) ? \mathbbZ[x]{P(x)\in\mathbb{Z}[x]} is of degree m and there are m rational integer values a for which 0 < |P(a)| < 2^−N N! where N=ém/2ù{N=\lceil m/2\rceil}, then P(x) is irreducible. A great number of authors have published results of Schur-type or Pólya-type afterwards. Our paper contains various extensions, generalizations and improvements of results from the literature. To indicate some of them, in Theorem 3.1 a Pólya-type result is established when the ground ring is the ring of integers of an arbitrary imaginary quadratic number field. In Theorem 4.1 we describe the form of the factors of polynomials of the shape h(x) f(x) + c, where h(x) is a polynomial and c is a constant such that |c| is small with respect to the degree of h(x) f(x). We obtain irreducibility results for polynomials of the form g(f(x)) where g(x) is a monic irreducible polynomial of degree ≤ 3 or of CM-type. Besides elementary arguments we apply methods and results from algebraic number theory, interpolation theory and diophantine approximation.     

Application of cyclodextrins in environmental bioassays for soil

Based on our former experience on contaminant solubilisation and mobilisation in the process of soil remediation we used cyclodextrins as additives in environmental bioassays, for improving solubility and bioavailability of the contaminant in soil and as a consequence sensitivity of the bioassay. In this article we introduce the findings on the application of RAMEB (randomly methylated ??-cyclodextrin) for testing PCP (pentachlorophenol) in soil, in three bioassays: bacterial luminescence-inhibition test with Vibrio fischeri, protozoon growth inhibition test with Tetrahymena pyriformis, and Ames mutagenicity test. We applied RAMEB which has a high solubilising capacity on many typical soil contaminant and PCP, because contradictory results were published for its toxicity and mutagenicity. The RAMEB-aided Ames test, gave a sudden and expressed increase in the mutagenicity of PCP, however, Ames mutagenicity was negative without cyclodextrin (CD). Based on these results we tried to apply RAMEB for increasing sensitivity of other bioassays, such as acute toxicity tests with different test organisms. According to our results the effect of RAMEB on bioavailability and toxic effect depends not only on the K _ow value (octanol?Cwater partition coefficient) of the chemical substances, but also on the test organism, the water-content of the test-matrix and the applied concentration of RAMEB, as well as its ratio to PCP. We collected all the characteristics of the bioassays applied for PCP and some other contaminants and showed the measured effect data in comparison with each other. We found that in the complex system of soil and soil suspension, used in the bioassays, the interactions between soil solid, water and gaseous phases, as well as between the test organism and RAMEB result in K _ow dependent partition of the contaminant between solid and water phases of soil, RAMEB, and the test organism. The conclusion is that RAMEB undoubtedly has an influence on the fate and behaviour of the contaminant in soil and soil suspensions, and the direction of the RAMEB-induced changes depends on the effective concentration of the RAMEB in the bioassay, the time of contact, the type of test organism, and the characteristics of the RAMEB?Ccontaminant complex. In those cases, when RAMEB increased the effect of a contaminated environmental sample, this CD-induced increase can be considered as a ??realistic worse case?? situation, which can be very useful in risk assessment, resulting in a moderate overestimate in the value of environmental risk.