On removable singularities of locally solvable differential operators

We study removable sets of solutions of locally solvable partial differential operators with smooth coefficients and characterize them in terms of capacity in the sense of Harvey and Polking. For operators of order one we are able to give a geometric characterization of removable sets in terms of orbits in the sense of Sussmann. Oblatum 2-IX-1995 & 14-V-1996     

The mechanism of solvolysis of methyl perchlorate in hydroxylic solvents: calculation of the cavity terms

From standard Gibbs energies of transfer, corrected for cavity or nonelectrostatic effects, it is concluded that the solvolysis of methyl perchlorate takes place through a looser-than-usual S_N2 transition state with a charge separation of about 0.52 units.     

Deviations from the Curie-Weiss law in paramagnetic dysprosium and terbium-50% holmium

The magnetic susceptibilities of single crystal dysprosium and terbium-50% holmium have been measured in their paramagnetic phases. The effect of annealing has been investigated and heating the sample to ≈ 360 K for ≈ 18 h causes ≈ 4% reduction in χ₂₇₃. Abrupt departures from Curie-Weiss behaviour occur at ≈ 257, 227, 199 K in Dy, and at 250, 214 and 197 K in Tb-50% Ho, coinciding with previously observed anomalies in the thermal expansion. This behaviour is attributed to the presence of residual antiferromagnetic order in the paramagnetic phase which is perturbed when the periodicity of the helical spin structure, estimated from neutron diffraction data, is commensurate with the hexagonal crystal lattice.     

Electrochemical detection of Arachis hypogaea (peanut) agglutinin binding to monovalent and clustered lactosyl motifs immobilized on a polypyrrole film

Direct detection of peanut agglutinin/lactose interactions was realized by an electrochemical approach based on a polypyrrole coated electrode displaying pendant carbohydrates.     

Fluorescent Properties of a Hybrid Cadmium Sulfide-Dendrimer Nanocomposite and its Quenching with Nitromethane

A fluorescent hybrid cadmium sulphide quantum dots (QDs) dendrimer nanocomposite (DAB-CdS) synthesised in water and stable in aqueous solution is described. The dendrimer, DAB-G5 dendrimer (polypropylenimine tetrahexacontaamine) generation 5, a diaminobutene core with 64 amine terminal primary groups. The maximum of the excitation and emission spectra, Stokes’ shift and the emission full width of half maximum of this nanocomposite are, respectively: 351, 535, 204 and 212 nm. The fluorescence time decay was complex and a four component decay time model originated a good fit (χ = 1.20) with the following lifetimes: τ ₁ = 657 ps; τ ₂ = 10.0 ns; τ ₃ = 59.42 ns; and τ ₄ = 265 ns. The fluorescence intensity of the nanocomposite is markedly quenched by the presence of nitromethane with a dynamic Stern-Volmer constant of 25 M⁻¹. The quenching profiles show that about 81% of the CdS QDs are located in the external layer of the dendrimer accessible to the quencher. PARAFAC analysis of the excitation emission matrices (EEM) acquired as function of the nitromethane concentration showed a trilinear data structure with only one linearly independent component describing the quenching which allows robust estimation of the excitation and emission spectra and of the quenching profiles. This water soluble and fluorescent nanocomposite shows a set of favourable properties to its use in sensor applications.     

Fluorescent Carbon Dots Capped with PEG<Subscript>200</Subscript> and Mercaptosuccinic Acid

The synthesis and functionalization of carbon nanoparticles with PEG₂₀₀ and mercaptosuccinic acid, rendering fluorescent carbon dots, is described. Fluorescent carbon dots (maximum excitation and emission at 320 and 430 nm, respectively) with average dimension 267 nm were obtained. The lifetime decay of the functionalized carbon dots is complex and a three component decay time model originated a good fit with the following lifetimes: τ ₁ = 2.71 ns; τ ₂ = 7.36 ns; τ ₃ = 0.38 ns. The fluorescence intensity of the carbon dots is affected by the solvent, pH (apparent pK _a of 7.4 ± 0.2) and iodide (Stern-Volmer constant of 78 ± 2 M⁻¹).     

Quasi-Hadamard Full Propelinear Codes

In this paper, we give a characterization of quasi-Hadamard groups in terms of propelinear codes. We define a new class of codes that we call quasi-Hadamard full propelinear codes. Some structural properties of these codes are studied and examples are provided.