Transport Properties of Random Walks on Scale-Free/Regular-Lattice Hybrid Networks

We study numerically the mean access times for random walks on hybrid disordered structures formed by embedding scale-free networks into regular lattices, considering different transition rates for steps across lattice bonds (F) and across network shortcuts (f). For fast shortcuts (f/F≫1) and low shortcut densities, traversal time data collapse onto a universal curve, while a crossover behavior that can be related to the percolation threshold of the scale-free network component is identified at higher shortcut densities, in analogy to similar observations reported recently in Newman-Watts small-world networks. Furthermore, we observe that random walk traversal times are larger for networks with a higher degree of inhomogeneity in their shortcut distribution, and we discuss access time distributions as functions of the initial and final node degrees. These findings are relevant, in particular, when considering the optimization of existing information networks by the addition of a small number of fast shortcut connections.     

Measurement of time-of-flight distributions for wavelength-dependent IR laser-stimulated desorption

The wavelength dependence of CCl₄ desorption from multilayers condensed on a Ge substrate is investigated. The strong spectral selectivity of the desorption yield and of the temperatures determined from the time-of-flight distributions coincides with the linear infrared absorption spectrum.     

Archaeometry of sicilian glazed pottery

Petrographic and chemical analyses of the ceramic body of 114 majolica artefacts manufactured in Sicily over a wide time range (16th–-19th century) are presented. All the analysed samples, which belong to museums and private collections, were previously attributed to Sicilian workshops based on stylistic features evaluated by expert historians of art. Unambiguous identification of the production sites of majolica handicrafts in Sicily remains, however, open to question when this relies only on purely stylistic considerations. To this end compositional and/or textural markers have been searched for in the ceramic body of the majolica artefacts in order to differentiate between the centres of manufacture which were active in Sicily in previous centuries. The study of thin sections has allowed the characterization of the raw materials as well as the microscopic fabric of manufacture from four of the more relevant Sicilian production sites, namely: Caltagirone, Sciacca, Palermo and Santo Stefano di Camastra. Chemical data, including minor and trace elements, have been submitted to computer assisted multivariate statistical techniques. Principal component analysis (PCA) and linear discriminant analysis (LDA) have defined compositional ceramic reference groups and, consequently, have enabled a more realistic discrimination of provenance. These data have documented several imports of majolica from Naples, while the same artefacts were previously attributed to Sicilian workshops, based on stylistic considerations . PACS 81.05.Je; 82.80.-d; 91.60.Mk     

Nucleophilic epoxidation of gamma-hydroxyvinyl sulfoxide derivatives

The nucleophilic epoxidation of simple (gamma-silyloxy)vinyl sulfoxides takes place with complete stereocontrol and high yields. For substrates bearing an additional substituent at the gamma position, a reinforcing/nonreinforcing scenario is operative. While E and Z silylated substrates undergo a primarily sulfur directed epoxidation with good to excellent diastereocontrol, the related (E)-(2-methoxyethoxy)methyl ethers display diminished selectivity for the diastereomer derived from the nonreinforcing scenario.     

Start-up Flow of a Bingham Fluid in a Pipe

We present an analytical solution of axisymmetric motion for a Bingham fluid initially at rest subjected to a constant pressure gradient applied suddenly. Using the Laplace transform, we obtain expressions which allow the calculation of the instantaneous velocity, plug radius and rate of flow as a function of time. We also give a relation for the shear stress in the plug and in the region where the behaviour of the fluid is Newtonian.     

Characterization and Validation of a Platinum Paper-based Potentiometric Sensor for Glucose Detection in Saliva

A paper-based potentiometric sensor was constructed and characterized for the detection of glucose in saliva. Dilution of the samples was optimized to afford the optimum experimental conditions of measurements. The performance allows for detecting abnormal high glucose concentrations observed in diabetes patients. Repeatability data were presented and the performance of the sensor compared to literature examples showing suitable characteristics at a much lower cost. The validation in real saliva samples was performed against a commercial colorimetric kit showing that glucose could be effectively determined in the 4–10 mM range based on the comparison with a reference method.     

Enantioselective Rhodium(I) Donor Carbenoid‐Mediated Cascade Triggered by a Base‐Free Decomposition of Arylsulfonyl Hydrazones

The reaction of diyne arylsulfonyl hydrazone substrates under rhodium(I)/BINAP catalysis gives access to sulfonated azacyclic frameworks in a highly enantioselective manner. This new cascade process considerably increases the molecular complexity by generating two C?C bonds, one C?S bond, and one C?H bond. Theoretical calculations, competitive experiments, and deuterium labeling have jointly been used to propose a mechanism that accounts for the reaction. The mechanism involves the formation of vinyl rhodium carbenoids, hydride migratory insertion, and intermolecular stereoselective nucleophilic attack. The last two steps are the key to the stereoselectivity of the process.     

Hybrid SSF/SHF Processing of SO<Subscript>2</Subscript> Pretreated Wheat Straw—Tuning Co-fermentation by Yeast Inoculum Size and Hydrolysis Time

Wheat straw is one of the main agricultural residues of interest for bioethanol production. This work examines conversion of steam-pretreated wheat straw (using SO₂ as a catalyst) in a hybrid process consisting of a short enzymatic prehydrolysis step and a subsequent simultaneous saccharification and fermentation (SSF) step with a xylose-fermenting strain of Saccharomyces cerevisiae. A successful process requires a balanced design of reaction time and temperature in the prehydrolysis step and yeast inoculum size and temperature in the SSF step. The pretreated material obtained after steam pretreatment at 210 °C for 5 min using 2.5 % SO₂ (based on moisture content) showed a very good enzymatic digestibility at 45 °C but clearly lower at 30 °C. Furthermore, the pretreatment liquid was found to be rather inhibitory to the yeast, partly due to a furfural content of more than 3 g/L. The effect of varying the yeast inoculum size in this medium was assessed, and at a yeast inoculum size of 4 g/L, a complete conversion of glucose and a 90 % conversion of xylose were obtained within 50 h. An ethanol yield (based on the glucan and xylan in the pretreated material) of 0.39 g/g was achieved for a process with this yeast inoculum size in a hybrid process (10 % water-insoluble solid (WIS)) with 4 h prehydrolysis time and a total process time of 96 h. The obtained xylose conversion was 95 %. A longer prehydrolysis time or a lower yeast inoculum size resulted in incomplete xylose conversion.