An experimental and theoretical study of the carbazole to carbazole intramolecular energy transfer in N‐vinylcarbazole/vinyl tert‐butyl‐benzoate copolymers of different molar compositions

Fluorescence depolarization and quenching measurements of N‐vinyl carbazole/vinyl tert‐butyl‐benzoate copolymers in dilute solution of several fluid solvents and in a rigid poly(methyl methacrylate) matrix were performed to study the effect of copolymer composition on the intramolecular energy transfer (IET) between carbazole groups (Cz) along the polymer chain. IET efficiency, as the amount of Cz? Cz intramolecular excimer formation, monotonically increases with Cz content up to a number average sequence length of carbazole of ca 12 (Cz molar content ≥ 90%). After this value, IET efficiency remains almost constant. Molecular dynamics simulations on isotactic and syndiotactic copolymer fragments of several monomer compositions were used for obtaining different parameters related to the efficiency for the IET process between Cz units along the polymer chain. Copyright © 2011 Society of Chemical Industry     

Effect of Hanger Flexibility on Dynamic Response of Suspension Bridges

Linearized continuum models of a suspended span with unloaded backstays and of a symmetric three-span suspension bridge are used to study the effects of the flexibility of the hangers on the vertical vibrations of suspension bridges. The models include elastic parabolic cables, flexible distributed hangers with variable length, and a stiffening girder represented by an elastic beam. It is shown that the free vibrations of a suspended span with unloaded backstays are controlled by five dimensionless parameters, while six dimensionless parameters control the response of a symmetric three-span suspension bridge. The results indicate that the flexibility of the hangers has a significant effect on the natural frequencies of the higher modes only when the relative stiffness of the girder is very high. The effects of hanger flexibility on the response of a suspension bridge to localized impulsive loads are also found to be small. These findings confirm the traditional, albeit previously untested, assumption of inextensible hangers. Finally, the threshold amplitudes of free vibrations that would result in the incipient slackening of the hangers are determined.     

Effect of Zn addition on the structure and electrochemical properties of co-doped BaCe0.6Zr0.2Ln0.2O3-δ (Ln=Y,Gd, Yb) proton conductors

In this work, BaCe_0.6Zr_0.2Y_0.2-xYb_xO_3-δ and BaCe_0.6Zr_0.2Gd_0.2-xYb_xO_3-δ (x?=?0–0.20), proton conducting materials are prepared by the freeze-drying precursor method. The sintering conditions were optimized by adding Zn(NO₃)₂·6H₂O as sintering additive. The materials are thoroughly characterized by different structural and microstructural techniques, including X-ray diffraction, scanning and transmission electron microscopy, and thermogravimetric-differential thermal analysis. The addition of Zn favours the phase formation and densification at lower sintering temperatures; however, it leads to the segregation of a Zn-rich secondary phase, with general formula BaLn₂ZnO₅ (Ln?Y, Gd and Yb), which is identified and quantified for the first time. All samples with Zn as sintering aid exhibit cubic structure; however, the samples without Zn crystallize with orthorhombic or cubic structure, depending on the composition and thermal treatment. The electrical properties are studied by impedance spectroscopy. A deep analysis of the bulk and grain boundary contributions to the conductivity has revealed that the bulk conductivity remains almost unchanged along both series over Yb-doping; however, the grain boundary resistance decreases. The highest conductivity values are found for the intermediate members of both series, BaCe_0.6Zr_0.2Y_0.1Yb_0.1O_3-δ and BaCe_0.6Zr_0.2Gd_0.1Yb₁O_3-δ, with 33 and 28?mS?cm^?1 at 750?°C, respectively.     

On multivariate order statistics. Application to ranked set sampling

Two new concepts of order statistics for multivariate samples are introduced. In one of the versions it turns out that not every multivariate order statistic is present in every sample. These order statistics have application in multivariate ranked set sampling and can be used to generate broad classes of multivariate densities in the sense of Jones. In this case the likelihood for the sample values and their corresponding ranks can be calculated based on the conditional density of a multivariate order statistics given its sample value, and such that its integral gives the probability for the multivariate order statistics under discussion to be observed. An alternative version of multivariate order statistics is also introduced, for which multivariate order statistics are always well defined and expressions for their marginal densities are derived. Since these multivariate order statistics are tailor made for multivariate ranked set sampling, their densities allow for parameter inference based on ranked set sampling. Some simulations show that both multivariate order statistics densities can be used with advantage with respect to simple random sampling.     

Oil and fungal biomass dispersion in a stirred tank containing a simulated fermentation broth

The production of γ‐decalactone by the filamentous fungus Trichoderma harzianum involves four phases (oil–water–air–mycelium) and its dispersion is crucial during fermentation. Oil and biomass (when present) dispersion, as a function of the volumetric power drawn (P/V), was characterized, in two; three‐ and four‐phase systems agitated with Rushton turbines. Trichoderma harzianum mycelium was used as the solid phase in the four‐phase system. Two stages of the fermentation were simulated: the beginning (15% oil and 1.4 kgm^?3 of mycelium) and the end (2% oil and 10.6 kg m^?3 of mycelium). In the two‐phase system, the use of exhausted broth achieved higher oil dispersions at low P/V values as compared with distilled water. Aeration decreased the oil dispersion for the high‐oil system, but enhanced oil dispersion for the low‐oil system. Compared with the P/V used in the actual fermentation (0.2 kW m^?3), a high segregation of the system was observed for the high‐oil/low‐biomass system, due to the difficulty of mixing the thick oil–air emulsion present at the top of the tank. The system simulating the end of the fermentation reached almost complete homogeneity of oil and biomass, a phenomenon due to the high biomass/oil ratio and the biomass acting as an oil carrier. © 2001 Society of Chemical Industry     

Riparian Vegetation Mapping for Hydraulic Roughness Estimation Using Very High Resolution Remote Sensing Data Fusion

For detailed hydraulic modeling, accurate spatial information of riparian vegetation patterns needs to be derived in automatic fashion. We propose a supervised classification for heterogeneous riparian corridors with a low number of spectrally separate classes using data fusion of a Quickbird image and LIDAR data. The approach considers nine land cover classes including three woody riparian species, brush, cultivated areas, grassland, urban infrastructures, bare soil and water. The classical “stacked vector” approach is adopted for data fusion, while the nonparametric weighted feature-extraction method and the pixel-oriented maximum likelihood algorithm are used for feature-reduction and classification purposes, respectively. We test the approach over a 14-km stretch of the Sieve River (Tuscany Region, Italy). A one-dimensional river modeling is applied over the study reach comparing the results of a classification-derived hydraulic roughness map and a traditional ground-based approach. Despite the complex study reach, the classification method produced encouraging accuracies (OKS = 0.77) and represents a useful tool to delineate application domains of flow resistance models suited to different hydrodynamic patterns (e.g., stiff/flexible vegetation). Hydraulic modeling results showed that the remotely derived floodplain roughness parameterization captures the equivalent Manning coefficient over 20 test cross sections with uncertainty distributions described by low mean and standard deviation values.     

Uptake of Tritiated Liquids by Individual Breakfast Cereal Flakes

ABSTRACT: Surface liquid adhesion (SLA) and liquid absorption (LA) of tritiated liquids, including water and skim, low-fat, whole, and fat-enriched milks, by cornflakes (CF) and frosted flakes (FF) were determined by scintillation counting using water-[³H] at 0.5 μCi/mL. SLA or the liquid adhering to individual flakes after a short immersion period was the same for CF and FF in the case of water (approximately 0.011 μL mm⁻² of flake) but were always higher for CF than for FF and increased as the fat content in milks augmented. LA of individual flakes, followed for 300 s of soaking, increased with time and was always higher for CF than for FF (for the same liquid), however, data did not follow a regular pattern. Flakes showed quite compact outer surfaces and an internal porous matrix composed of air cells of various sizes separated by dense walls of different thicknesses. This heterogeneous microstructure of individual flakes may be the cause of the lack of a simple kinetics during the soaking process. Previous results obtained by soaking a mass of flakes overestimated the uptake of fluid by individual because they included the liquid occluded between the flakes.     

One year of ICTP diploma courses on-line using the automated EyA recording system

The 12-month pre-Ph.D. ICTP Diploma Courses in the fields of Condensed Matter Physics, High Energy Physics, Mathematics, Earth System Physics and Basics Physics have been recorded using the automated, low cost recording system called EyA developed in-house. We discuss the technical details on how these recordings were implemented, together with some web usage statistics and students feedback. As yet, no similar endeavor has been made to put on-line a complete high-level Diploma Programme, due to the high costs involved when using alternative recording solutions. These recordings are freely available on the website www.ictp.tv.