Fractional products of sets

For integers d > 1 and arbitrary 1 ? α ? d, α-products in d-fold Cartesian products are produced by probabilistic methods. Some explicit constructions are given by solutions of instances of the Turán problem for graphs.     

A novel labdane diterpene from Acritopappus longifolius

A novel labdane diterpene was isolated from the plant Acritopappus longifolius. The structure of this compound was established by 1D- and 2D-nuclear magnetic resonance spectroscopic techniques and mass spectrometry data. N-Methyl-4-hydroxy-trans-proline, stigmasterol-3-O-β-d-glycoside, and the flavonoids quercetin, luteolin, kaempferol, and rutin were also isolated.     

An electronic tongue for gliadins semi-quantitative detection in foodstuffs

An all-solid-state potentiometric electronic tongue with 36 polymeric membranes has been used for the first time to detect gliadins, which are primarily responsible for gluten intolerance in people suffering from celiac disease. A linear discriminant model, based on the signals of 11 polymeric membranes, selected from the 36 above using a stepwise procedure, was used to semi-quantitatively classify samples of a “Gluten-free” foodstuff (baby milked flour), previously contaminated with known amounts of gliadins (<10, 20-50 or >50 mg/kg), as “Gluten-free”, “Low-Gluten content” or “Gluten-containing”. For this food matrix, the device had sensitivity towards gliadins of 1-2 mg/kg and overall sensitivity and specificity of 77% and 78%, respectively. Moreover, the device never identified an ethanolic extract containing gliadins as “Gluten-free”. Finally, the system also allowed distinguishing “Gluten-free” and “Gluten-containing” foodstuffs (15 foods, including breads, flours, baby milked flours, cookies and breakfast cereals) with an overall sensitivity and specificity greater than 83%, using the signals of only 4 selected polymeric membranes (selected using a stepwise procedure). Since only one “Gluten-containing” foodstuff was misclassified as “Gluten-free”, the device could be used as a preliminary tool for quality control of foods for celiac patients.     

Optical and structural properties of ZnO nanorods grown by pulsed laser deposition without a catalyst

Pulsed laser deposition without a catalyst is used to grow ZnO nanorods less than 10 nm in diameter. The structure of the rods is studied by Raman scattering during excitation in the visible and UV regions. The temperature dependences of exciton spectra and the behavior of green luminescence are investigated in the temperature range 10–280 K. At room temperature, the luminescence intensity of the ZnO nanorods in the exciton region is higher than the green luminescence intensity by a factor of 7.8.     

Analytical study of non-linear transport across a semiconductor-metal junction

In this paper we study analytically a one-dimensional model for a semiconductor-metal junction. We study the formation of Tamm states and how they evolve when the semi-infinite semiconductor and metal are coupled together. The non-linear current, as a function of the bias voltage, is studied using the non-equilibrium Green’s function method and the density matrix of the interface is given. The electronic occupation of the sites defining the interface has strong non-linearities as a function of the bias voltage due to strong resonances present in the Green’s functions of the junction sites. The surface Green’s function is computed analytically by solving a quadratic matrix equation, which does not require adding a small imaginary constant to the energy. The wave function for the surface states is given.     

New constituents from Mikania laevigata Shultz Bip. ex Baker

A new phenylpropanoid and two new diterpenes were isolated from the leaves of the plant Mikania laevigata Shultz Bip. ex Baker. The structures of these compounds were established by 1D- and 2D-nuclear magnetic resonance spectroscopic techniques and mass spectrometry data. Taraxerol, lupeol, coumarin, syringaldehyde, trans-melilotoside, cis-melilotoside, adenosine, patuletin 3-O-β-d-glucopyranoside, kaempferol 3-O-β-d-glucopyranoside, quercetin 3-O-β-d-glucopyranoside, methyl 3,5-di-O-caffeoyl quinate, and 3,3′,5-trihydroxy-4′,6,7-trimethoxyflavone were isolated too. In addition, the compounds dihydrocoumarin, spathulenol, caryophyllene oxide, kaurenoic acid, beyerenoic acid, and lupeol acetate were identified by GC-MS.     

Ultrasound promoted synthesis of 5-hydroxy-5-trihalomethyl-4,5-dihydroisoxazoles and beta-enamino trihalomethyl ketones in water

A convenient method for the preparation of 5-hydroxy-5-trihalo-4,5-dihydroisoxazoles and beta-enamino trihalomethyl ketones, from the reaction of 1,1,1-trihalo-4-alkoxy-3-alken-2-ones with hydroxylamine and anilines, respectively, using water as solvent and under ultrasound irradiation is reported.     

Optical and structural studies in Eu-implanted AlN films

Eu ions were incorporated into AlN thin films using ion implantation, and the influence of the post-implant annealing ambient on structural and optical properties was investigated. Eu is incorporated into lattice sites which are slightly displaced from the substitutional Al sites. When compared with the as-implanted sample the near-substitutional ion fraction is reduced due to the thermal annealing in different atmospheres. The AlN crystal quality does not change with different annealing conditions, but sensitive defect-related emission bands are developed under different annealing temperatures. Eu³⁺ optical activation is detected for all the annealed samples. No spectral changes are observed for the shape of the intra- transition, suggesting that a similar site symmetry is preserved even when a slight displacement from the substitutitional site of the Eu³⁺ ions occurs. The role of the annealing conditions on the spectral position and thermal quenching of the transition is discussed.     

Electronic properties of graphene multilayers

We study the effects of disorder in the electronic properties of graphene multilayers, with special focus on the bilayer and the infinite stack. At low energies and long wavelengths, the electronic self-energies and density of states exhibit behavior with divergences near half filling. As a consequence, the spectral functions and the conductivities acquire anomalous properties. In particular, we show that the quasiparticle decay rate has a minimum as a function of energy, there is a universal minimum value for the in-plane conductivity of order e(2)/h per plane and, unexpectedly, the c-axis conductivity is enhanced by disorder at low doping, leading to an enormous conductivity anisotropy at low temperatures.     

The critical random graph,with martingales

We give a short proof that the largest component C ₁ of the random graph G(n, 1/n) is of size approximately n ^2/3. The proof gives explicit bounds for the probability that the ratio is very large or very small. In particular, the probability that n ^−2/3|C ₁| exceeds A is at most e ^{- cA3}{e^{ - c{A^3}}} for some c > 0.