Characterization of natural cellulosic fibers from Yucca aloifolia L. leaf as potential reinforcement of polymer composites

Cellulose - In this work lignocellulosic fibers were obtained from Yucca aloifolia L. leaves and their chemical, morphological, thermal and mechanical properties were studied. The fibers were...     

Thermal analysis of the combustion of charcoals from Eucalyptus dunnii obtained at different pyrolysis temperatures

DSC and TG/DTA were used to study charcoals obtained from eucalyptus wood at different pyrolysis temperatures, as well as the exchanged energy, and the transformations involved during the pyrolysis process. Charcoals DSC curves showed two exothermic peaks, at ~610 and ~750 K. The first peak was squashed for those charcoals obtained at higher final pyrolysis temperatures, and it disappeared in the charcoals obtained at 873 and 923 K. The second peak intensity increased and its location changed at the higher temperatures. Charcoal characterization showed a rise of heat values with the pyrolysis temperature.     

Quartz Crystal Microbalance monitoring the real-time binding of lectin with carbohydrate with high and low molecular mass

A Quartz Crystal Microbalance (QCM) was used to monitor the mass changes on a quartz crystal surface containing immobilized lectins that interacted with carbohydrates. The strategy for lectin immobilization was developed on the basis of a multilayer system composed of Au–cystamine–glutaraldehyde–lectin. Each step of the immobilization procedure was confirmed by FTIR analysis. The system was used to study the interactions of Concanavalin A (ConA) with maltose and Jacalin with Fetuin. The real-time binding of different concentrations of carbohydrate to the immobilized lectin was monitored by means of QCM measurements and the data obtained allowed for the construction of Langmuir isotherm curves. The association constants determined for the specific interactions analyzed here were (6.4 ± 0.2) × 10⁴ M^− 1 for Jacalin–Fetuin and (4.5 ± 0.1) × 10² M^− 1 for ConA–maltose. These results indicate that the QCM constitutes a suitable method for the analysis of lectin–carbohydrate interactions, even when assaying low molecular mass ligands such as disaccharides.     

Inverse photoinduced electron transfer in large betaine molecules

We have used ab initio methods to confirm the existence of an inversion in the photoinduced intramolecular electron transfer in large conjugated pyridinium betaines, by examining compounds where an imidazole ring and a pyridinic group are connected by polyenic chains of increasing size. As these intermediary conjugated bridges get longer, an unusual net charge transfer is observed. The conjugated chain becomes a channel for the photoinduced electronic density flow, and the amount of charge at the donor and acceptor groups is reduced, while an inversion in the spatial localization of the frontier orbitals occurs. We discuss the corresponding implications on the nonlinear optical, photochemical and solvatochromic properties of these molecules.     

A contribution to the global formulation of the higher-order Poincaré-Cartan form

The global formulation of the higher-order Poincaré-Cartan form for Lagrangian field theories in the calculus of variations is re-examined in terms of the theory of lifts of tensor fields on a manifold to its higher-order prolongated jet bundles.Partially supported by CNPq, Brazil, Proc. MA 30.1115/79.     

Analysis of effective service time with age dependent interruptions and its application to optimal rollback policy for database management

A stochastic model is developed describing a service system subject to inhomogeneous Poisson interruptions with age dependent interruption periods. By studying the probabilistic flow of the underlying multivariate Markov process, the Laplace transform of the effective service time is explicitly obtained. For general renewal interruptions, only the expected effective service time is derived. As an application, an optimal checkpoint policy is examined for database management. It is shown that an optimal policy maximizing the ergodic availability of the database is to implement a checkpoint as soon as the cumulative uptime of the database reaches a prespecified constantk ^*. A computational procedure is then developed for findingk ^* and numerical results are exhibited.This work was supported in part by the National Science Foundation under Grant No. ECS-8600992 and by the IBM Program of Support for Education in the Management of Information Systems.     

A simple and general preparation of vinylic sulfides, selenides and tellurides

A general method for the synthesis of vinylic chalcogenides by nucleophilic and Ni-catalyzed vinylic substitution on vinylic halides by phenyl chalcogenolates is described. The reactions were regio and stereoselective for the nickel catalyzed substitution, and mixture of isomers was observed for some examples in the thermal process in DMF.     

Thionicotinamide SAM on Gold: Adsorption Studies and Electroactivity

STM and impedance results of the self‐assembled monolayer (SAM) formed with thionicotinamide (TNA) on gold indicate the presence of defects that increase with the immersion time of the electrode in the TNA solution affecting the SAM electroactivity toward the electron transfer reaction of the cytochrome c metalloprotein and [Fe(CN)₆]^4? and [Ru(NH₃)₆]³⁺ complexes. It was observed that this electroactivity was also affected by the pH of the electrolyte solution. SERS and STM data indicate sulfur coordination to the surface with contribution of the NH₂ group. From the dependence of the TNA surface coverage on the temperature and concentration in solution, thermodynamic parameters of adsorption were determined.