Ferromagnetism and metal-insulator transition in the disordered Hubbard model

A detailed study of the paramagnetic to ferromagnetic phase transition in the one-band Hubbard model in the presence of binary-alloy disorder is presented. The influence of the disorder (with concentrations x and 1-x of the two alloy ions) on the Curie temperature T(c) is found to depend strongly on electron density n. While at high densities, n>x, the disorder always reduces T(c); at low densities, n相似文献   

Counter-Ion Influence on Polypyrrole Potentiometric pH Sensitivity

The pH sensitivity of conducting polymer films is an important issue from the sensor design point of view. The doping and supporting electrolyte anions effect on the potentiometric sensitivity and response time of polypyrrole (PPy) electrodes towards changes of solution pH were studied. It was found that (i) the response of PPy doped by easily exchangeable common anions (Cl^–, NO₃ ^–, ClO₄ ^–) in their solutions (KCl, KNO₃, NaClO₄) is slow. In contrast, (ii) polypyrrole films deposited in the presence of weak acid anions (phthalates, oxalates, salicylates) were characterised by instantaneous responses in the above mentioned solutions. On the basis of electrochemical experiments (open circuit potential vs. time dependencies, cyclic voltammetry, EQCM), the observed differences were attributed to different mechanisms of pH sensitivity of tested films. The long response times are related to the incorporation of the solution ions into the film in order to compensate charges created due to protonation. On the other hand, if the ion-exchange is hindered as in the case of (ii), instantaneous open circuit responses are observed due to polarisation of the oxidised polymer layer, analogously to the metal electrode. Moreover, for these films the internal pH buffering within the polymer membrane will weaken the pH change effect.The mechanisms were confirmed in the course of studying the pH effect in solutions containing anions easily (KCl, NaClO₄, KNO₃) or hardly exchangeable with polypyrrole (K₂SO₄, sodium poly(4-styrenesulphonate) solutions) acidified with H₂SO₄.     

Key Word Index of Volume 38 – 2003

Other Index

Key Word Index of Volume 38 – 2003     

An efficient synthesis of vinylsilanes from acylsilanes and alkyl 1-phenyl-1H-tetrazol-5-yl sulfones. Brook vs Smiles rearrangement

[reaction: see text] Vinylsilanes are formed in high yields in the reaction of representative acyl(trimethyl)silanes with anions generated from Kocienski's sulfones.     

Gas chromatography with mass spectrometric,atomic emission and Fourier transform infrared spectroscopic detection as complementary analytical techniques for the identification of unknown impurities in pharmaceutical analysis

An example of the complementary use of GC-MS. GC-AED and GC-FT-IR is described for efficient structure elucidation of an unknown impurity in pharmaceutical analysis. None of the analytical techniques could solve the structure of the unknown impurity alone; identification was, however, straightforward by combining the available spectroscopic information. GC-MS provided information about structural fragments and molecular mass of the unknown compound. GC-AED was used for confirmation of the occurrence of the individual elements in the structure and to enable calculation of the empirical formula. GC-FT-IR gave valuable information regarding functional groups in the molecule.     

Molecular dynamics of 5-HT1A and 5-HT2A serotonin receptors with methylated buspirone analogues

In the present study experimentally determined ligand selectivity of three methylated buspirone analogues (denoted as MM2, MM5 and P55) towards 5-HT_1A and 5-HT_2A serotonin receptors was theoretically investigated on a molecular level. The relationships between the ligand structure and 5-HT_1A and 5-HT_2A receptor affinities were studied and the results were found to be in agreement with the available site-directed mutagenesis and binding affinity data. Molecular dynamics (MD) simulations of ligand-receptor complexes were performed for each investigated analogue, docked twice into the central cavity of 5-HT_1A/5-HT_2A, each time in a different orientation. Present results were compared with our previous theoretical results, obtained for buspirone and its non-methylated analogues. It was found that due to the presence of the methyl group in the piperazine ring the ligand position alters and the structure of the ligand-receptor complex is modified. Further, the positions of derivatives with pyrimidinyl aromatic moiety and quinolinyl moiety are significantly different at the 5-HT_2A receptor. Thus, methylation of such derivatives alters the 3D structures of ligand-receptor complexes in different ways. The ligand-induced changes of the receptor structures were also analysed. The obtained results suggest, that helical domains of both receptors have different dynamical behaviour. Moreover, both location and topography of putative binding sites for buspirone analogues are different at 5-HT_1A and 5-HT_2A receptors.     

Poisson integrals and Riesz transforms for Hermite function expansions with weights

We consider expansions with respect to the multi-dimensional Hermite functions which are eigenfunctions of the harmonic oscillator L=−Δ+|x|². For the heat-diffusion and Poisson semigroups corresponding to a self-adjoint extension of L we investigate their boundary behaviour and mapping properties. All this is done for functions from L^p(w), 1?p<∞, w∈A_p. Then Riesz transforms and conjugate Poisson integrals are considered. The Riesz transforms occur to be Calderón-Zygmund operators hence their mapping properties follow by using results from a general theory.     

On odd points and the volume of lattice polyhedra

Denote by _n ³ ,n 2, the lattice consisting of all pointsx in ³ such thatnx belongs to the fundamental lattice ³ of points with integer coordinates. Letl _n be the subset of _n ³ consisting of all points whose coordinates are odd multiples of 1/n. The purpose of this paper is to give several new Pick-type formulae for the volume of three-dimensional lattice polyhedra, that is, polyhedra with vertices in ³. Our formulae are in terms of numbers of only thel _n-points belonging to a lattice polyhedronP in contrast to already known formulae which employ numbers of all the _n ³ -points inP. On our way to establishing the formulae we show that the number of points froml _n belonging to a three-dimensional lattice polyhedronP has some polynomiality properties similar to those of the well-known Ehrhart polynomial expressing the number of points of _n ³ inP. The paper contains also some comments on a problem of finding a volume formula which would employ only the setsl _n and which would be applicable to lattice polyhedra in arbitrary dimensions.Research partially supported by KBN Grant 2 P03A 008 10.     

Cassie's Law and Concavity of Wall Tension with Respect to Disorder

For the semiinfinite Ising model with quenched boundary disorder, we prove concavity inequalities for the difference of wall tensions associated with the minus and plus phases. These inequalities generalize phenomenological equalitiesknown as Cassie's law.