Helicon waves in semiconductor superlattices

The dispersion relation for the helicon frequency of a system consisting of a periodic array of two-dimensional gas layers is studied as a function of both q and q_z, the components of the wavevector parallel and perpendicular to the layers. The result is compared with that for a homogeneous three-dimensional electron gas.     

Investigations on the Stability of Plasma Modified Silicone Surfaces

In this work it was investigated the effect of the exposure to different plasmas on the wettability of silicone samples. We have observed that oxygen. argon, and hydrogen glow discharges are quite effective in reducing the water contact angle of such polymer. However, indifferently to efficiency of the treatment, practically all the modified surfaces recovered great part of their original hydrophobicity. We have investigated this hydrophobic recovery using surface energy measurements and theoretical simulations based on the exponential decay of the population of polar groups on the surface. According to our results such recovery can be attributed to the decrease of polar species at the interface water–polymer surface.     

Quality and Human Health Risk Assessment of Metals and Nitrogen Compounds in Drinking Water from an Urban Area Near a Former Non-Ferrous Ore Smelter

The quality and potential health risk of drinking waters in Medias, a town near a former non-ferrous ore smelter in Romania, was assessed using the drinking water quality index (DWQI), hazard quotient (HQ) and total hazard quotient (THQ). A total of 29 water samples collected from 26 wells and 3 springs used as drinking water sources, located in near proximity to agricultural, industrial or household contamination sources, were characterized. The obtained results indicated high NO₂^?, NO₃^?, Cd and Mn levels that exceeded the corresponding maximum allowable concentrations. According to the DWQI values, only 10% of water sources have acceptable quality, while 21% are threatened, and 69% have poor- quality. The health risk assessment suggested a high risk for NO₃^? for more than 72% of the drinking waters HQ_NO3^??>?1.0 but no risk for metals and NO₂^? (HQ_metals< 1.0; HQ_NO2^?< 1.0).     

Mechanochemistry as a versatile and scalable tool for nanomaterials synthesis: Recent achievements in Košice,Slovakia

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Synthesis and properties of isoxazolo[60]fullerene-donor dyads

A series of isoxazolo[60]fullerenes has been prepared in one pot from aldoximes under microwave irradiation. Several donors and acceptors were used as substituents. The absorption and emission spectra of these compounds in polar solvents suggest a weak charge-transfer interaction between the oxygen atom of the isoxazoline moiety and the C(60) cage, as well as a stronger interaction between the donor and the fullerene cage when the attached groups are p-N,N-dimethylaniline or ferrocene. The electrochemical properties of the compounds were investigated and they show the same or better acceptor character than C(60) in all cases. Theoretical calculations support the results obtained. Solvent effects in the (1)H NMR spectra have been determined and provide useful information concerning the polarization of dyads.     

Photoisomerization pathways of 8,16-methno[2.2]metacyclopane-1,9-diene. A model case for adiabatic electrocyclic ring closure in the excited singlet state

The title compound 1b ideally meets the theoretical requirements for the occurrence of an adiabatic photoisomerization in the lowest excited state (¹ 1b *) and, indeed, the predominant primary photoreaction observed is the conversion to its fluorescent valence isomer 10b, 10c-methano-cis-10b 10c-dihydropyrene (¹ 1a *). The mechanism for the formation often previously observed photoproduct 8b, 9a-dihydro-9H - cyclopropa[e]pyrene ( 4a ) has been analyzed in some detail (Scheme). Below ? 30°C the reaction path consists of a three quantum process (two di-π-methane rearrangements and photochemical 1,7-H shift) involving two thermally stable, but light-sensitive isomers 8,11b-methanocyclodeca[cde]naphthalene ( 2b ) and 9H -cyclohepta[def]-phenanthrene ( 3b ). At room temperature the rearrangement 2b→4a proceeds with a single excitation step bypassing the ground state intermediate 3b . Finally, upon prolonged irradiation of ( 4a ), the methylene group is lost to yield pyrene. Compound 2b completes the series of all possible adducts of methylene to a C?C bond of pyrene.     

Inorganic nanocrystal self-assembly via the inclusion interaction of beta-cyclodextrins: toward 3D spherical magnetite

Synthesis and three-dimensional (3D) assembly of magnetite nanocrystals were realized by a one-pot procedure, in which Fe(acac)3 (acac = acetylacetonate) was partly reduced by hydrazine accompanied with ethylene glycol and spontaneously assembled into spherical nanostructures in the presence of surfactants including beta-cyclodextrin, oleic acid, and oleylamine. The size of the assembled spheres can coarsely be controlled in a limited range (100 nm to 2 microm) by changing the reaction temperature and the concentration of beta-cyclodextrin. X-ray diffraction and far Fourier transform infrared spectroscopy were employed to clarify the structures of magnetite in the assembled spheres. Electron diffraction pattern in a selected-area exhibits a high-crystallinity characteristic of cubic structure magnetite. We found that the formation of spherical magnetite aggregates highly depends on the presence of beta-cyclodextrin, while oleic acid and oleylamine improve the morphology of individual magnetite nanoparticles in the assembled spheres. In addition, the thermal gravimetric analysis and differential thermal analysis were applied to determine the content of magnetite in the products. Magnetic properties were also studied by using a superconducting quantum interference device magnetometer.