Nanoparticles from a Gold Complex with Sulfite Ion as Ligand: Preparation and Characterization

Gold colloidal nanoparticles (GNPs) were prepared by reducing a complex of Au⁺. Na₃Au(SO₃)₂ with sodium citrate. The procedure provides control of the dimension of nanoparticles produced, which is a function of reaction time and concentration of reactants. The nanoparticles were separated by centrifugation and their characteristics and dimensions were studied using UV-Vis and IR spectroscopy and transmission electronic microscopy (TEM).     

Fluorescent solar concentrators. Experimental results

A physical characterization is presented for classes of selected fluorescent substances, with special emphasis on their concentration in the support. The influence of climatic factors was analyzed from two points of view: spectral and structural. Two types of geometrical models of fluorescent solar concentrators have been obtained : plates and cylinders.     

On the electrical conduction in the interpolysilicon dielectriclayers

To reduce the low-field electrical conductivity of interpolysilicon dielectrics used in electrically erasable programmable read-only (EEPROM) memories devices, the roughness of the poly-SiO₂ interface until now has been decreased in two ways: (1) by increasing the temperature of oxidation and doping of polysilicon combined with low-pressure chemical vapor deposition (LPCVD) of silicon (undoped or in-situ doped) in the amorphous phase, or (2) by the use of LPCVD high-temperature oxide (HTO) deposited over polycrystalline silicon. The advantages of both methods are combined, and electrical conduction results for an interpoly structure based on LPCVD smooth surface polysilicon and LPCVD HTO SiO₂ are presented. The data are interpreted in terms of the Fowler-Nordheim mechanism     

Mechanochemically initiated polymerisations. 12. Spectral and thermal characterisation of some products obtained by vibratory milling of benzene and pyridine

Vibratory milling is used to open the aromatic ring of compounds such as benzene and pyridine and this is followed by concatenation of the structural units. The products obtained form both the soluble fractions in methanol, i.e. dimethylformamide and the insoluble fraction, the latter being found in the prevalent amount. Analysis of the soluble fractions by infrared spectroscopy (i.r.) and pyrolysis-gas chromatography (p.-g.c.) conforms their linear structure of the polyenic type with some short crosslinkings and a great sensitivity to the action of atmospheric oxygen.     

Dissipation in current-carrying high-Tcsuperconducting ceramics in applied magnetic field

The dissipation mechanism in high-T _csuperconducting ceramics was studied by analyzing the magnetic field dependence of the transport critical current and the form of the current-voltage characteristics. It was found that the actual magnetic field dependence of the transport critical current is significantly slower than that predicted by the weak-link-quenching model. The low-voltage-level current-voltage characteristics were described in terms of thermally activated flux creep at grain boundaries, taking into account collective pinning of intergranular Josephson vortices. For the investigated samples, a low-field, high-temperature mean pinning energy barrier of a few tens of meV was determined.     

Evidence for Irradiation Triggered Nonuniform Defects Distribution in Multiharmonic Magnetic Susceptibility of Neutron Irradiated YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−</Subscript><Subscript><Emphasis Type="Italic">δ</Emphasis></Subscript>

Multiharmonic ac-magnetic susceptibilityx ₁,x ₂,x ₃, of neutron irradiated Li-doped YBa₂Cu₃O_7−x has revealed a nonmonotonic dependence of all harmonics on the neutron fluence. The irradiation has a strongly depressive influence on the intergrain connection suggesting an increase of the effective thickness of the intergranular Josephson junction at a neutron fluence of 0.98 × 10¹⁷ cm⁻². Less damaged are the intragrain properties. A spectacular enhancement of the superconducting intragranular properties reflected in the characteristics of all harmonics was observed at highest fluence φ=9.98 × 10¹⁷ cm⁻². We assume that this effect results from the development of a space inhomogeneous distribution with alternating defectless and defect-rich regions.     

Bioactive polymers

Summary The immobilization of invertase on carboxymethyl cellulose acid chloride and the factors influencing the reaction (enzyme/support ratio, duration and pH) are studied. The activity of both coupled and free enzymes varies with temperature and pH of the incubation reaction. The values of the Michaelis-Menten constant are higher for the immobilized enzyme.     

Q-Based Design Equations and Loss Limits for Resonant Metamaterials and Experimental Validation

Practical design parameters of resonant metamaterials, such as loss tangent, are derived in terms of the quality factor Q of the resonant effective medium permeability or permittivity. Through electromagnetic simulations of loop-based resonant particles, it is first shown that the Q of the effective medium response is essentially equal to the Q of an individual resonant particle. This implies that by measuring the Q of a single fabricated metamaterial particle, the effective permeability or permittivity of a meta-material can be estimated simply and accurately without complex simulations, fabrication, or measurements. Experimental validation shows that the frequency-dependent complex permeability analytically estimated from the measured Q of a single fabricated self-resonant loop agrees with the complex permeability extracted from S parameter measurements of a metamaterial slab to better than 20 %. This Q equivalence reduces the design of a metamaterial to meet a given loss constraint to the simpler problem of the design of a resonant particle to meet a specific Q constraint. The Q-based analysis also yields simple analytical expressions for estimating the loss tangent of a planar loop magnetic metamaterial due to ohmic losses. It is shown that tan delta ap 0.001 is a strong lower bound for magnetic loss tangents for frequencies not too far from 1 GHz. The ohmic loss of the metamaterial varies inversely with the electrical size of the metamaterial particle, indicating that there is a loss penalty for reducing the particle size at a fixed frequency.