Radiation-Induced Synthesis of Fullerene-Silica Hybrid Nanomaterials

C₆₀ fullerene has been radiation grafted on bare and functionalized silica surface with mercaptopropyl moieties in toluene solution. The resulting fullerene-silica hybrid nanomaterials have been characterized by FT-IR and solid state ¹³C CP-MAS NMR spectroscopy and compared to the radiolysis products of C₆₀ in toluene. It has been found that fullerene is grafted on silica surface but, because the radiation grafting has been conducted in toluene, fullerene results arylated from radicals derived from toluene radiolysis. The fullerene-silica hybrid nanomaterials cannot be extracted by warm decalin, demonstrating that the fullerene cage is chemically bonded on the silica surface. The thermal behavior of fullerene-silica hybrid nanomaterials has been studied by thermogravimetric analysis (TGA) and differential thermal analysis (DTA) in air flow.     

Molecular features of sulfonic acids used for synthesis of overbased detergent additives

Overbased calcium sulfonates are used in many modern oil formulations to provide cleaning action and to neutralize the organic acids formed during combustion, preventing corrosion. The performance of detergents is related to their molecular structure, which is generally known only as a chemical category. In the present work, nuclear magnetic resonance (NMR) spectroscopy and electrospray ionization mass spectrometry are used to analyze the molecular structure of three alkyl‐benzene sulfonic acids in detail. Some important molecular features were obtained by elaborating the NMR signal intensities, such as the number and positions of alkyl substituents on the benzene ring, the distribution of alkyl chain lengths and the mole fraction of 1‐phenyl isomers (synthesized by alkylation of benzene with α‐olefin). Ion‐trap mass spectrometry is used to obtain the mass spectrometry/mass spectrometry (MS²) spectra of the principal molecular ions. By choosing suitable molecular ions, MS² spectra can ascertain the presence of different substituted benzene isomers within a mixture because the MS² spectra show specific fragments due to the number of alkyl substituents on the aromatic ring. Copyright © 2006 John Wiley & Sons, Ltd.     

Limitations on the uses of multimedia exposure measurements for multipathway exposure assessment--Part I: Handling observations below detection limits.

Multimedia data from two probability-based exposure studies were investigated in terms of how censoring of nondetects affected estimation of population parameters and associations. Appropriate methods for handling censored below-detection-limit(BDL)values in this context were unclear since sampling weights were involved and since bivariate associations/measures were of interest. Both simple substitution(e.g., using 1/2 or 2/3 of the detection limit(DL)for BDL values)and truncation-based strategies were investigated by creating some artificial DLs and comparing resultant estimates with the original studies'uncensored results. The substitution methods generally outperformed the truncation methods, with the(2/3)DL substitution generally performing best.     

Scalable Pareto set generation for multiobjective co-design problems in water distribution networks: a continuous relaxation approach

In this paper, we study the multiobjective co-design problem of optimal valve placement and operation in water distribution networks, addressing the minimization of average pressure and pressure variability indices. The presented formulation considers nodal pressures, pipe flows and valve locations as decision variables, where binary variables are used to model the placement of control valves. The resulting optimization problem is a multiobjective mixed integer nonlinear optimization problem. As conflicting objectives, average zone pressure and pressure variability can not be simultaneously optimized. Therefore, we present the concept of Pareto optima sets to investigate the trade-offs between the two conflicting objectives and evaluate the best compromise. We focus on the approximation of the Pareto front, the image of the Pareto optima set through the objective functions, using the weighted sum, normal boundary intersection and normalized normal constraint scalarization techniques. Each of the three methods relies on the solution of a series of single-objective optimization problems, which are mixed integer nonlinear programs (MINLPs) in our case. For the solution of each single-objective optimization problem, we implement a relaxation method that solves a sequence of nonlinear programs (NLPs) whose stationary points converge to a stationary point of the original MINLP. The relaxed NLPs have a sparse structure that come from the sparse water network graph constraints. In solving the large number of relaxed NLPs, sparsity is exploited by tailored techniques to improve the performance of the algorithms further and render the approaches scalable for large scale networks. The features of the proposed scalarization approaches are evaluated using a published benchmarking network model.     

¹H-NMR study of the impact of high pressure and thermal processing on cell membrane integrity of onions

Proton nuclear magnetic resonance (1H-NMR) relaxometry was used to study the effects of high pressure and thermal processing on membrane permeability and cell compartmentalization, important components of plant tissue texture. High pressure treated onions were subjected to pressure levels from 20 to 200 MPa at 5 min hold time at initial temperatures of 5 and 20 °C. Thermally treated onions were exposed for 30 min at temperatures from 40 to 90 °C. Loss of membrane integrity was clearly shown by changes in transverse relaxation time (T(2)) of water at temperatures of 60 °C and above. Destabilization effects on membranes exposed to high pressure were observed at 200 MPa as indicated by T(2) measurements and cryo-scanning electron microscopy (Cryo-SEM). T(2) relaxation successfully discriminated different degrees of membrane damage based on the T(2) shift of the vacuolar component. Analyses of the average water self-diffusion coefficient indicated less restricted diffusion after membrane rupture occurred in cases of severe thermal treatments. Milder processing treatments yielded lower average diffusion coefficients than the controls. 1H-NMR proved to be an effective method for quantification of cell membrane damage in onions and allowed for the comparison of different food processes based on their impact on tissue integrity.     

The investigation on cationic exchange capacity of zeolites: the use as selective ion trappers in the electrokinetic soil technique

The cation exchange capacity (CEC) of porous zeolites allows to adsorb in the framework cavities the cations as pollutant heavy metal ions. We investigate the CEC behaviour of different zeolites in different experimental conditions; in solution where the ion's mobility is spontaneous and free and in the electrokinetic system where the ion's mobility is driven by the electric field. The aim of this study is to investigate if the CEC is an useful property to create a special interface region of zeolites, that if placed in the electrokinetic cell, just before the cathode, could allow to capture and concentrate the heavy metallic ions, during their migrating process. The zeolite 13X investigated in the electrokinetic proofs, retains a good high ions adsorption, even if quite smaller than the relevant free solution condition and well acts as confined trap for the heavy metal ions. In fact no trace of metallic deposition are present on the electrode's surface.