Aromatic nitrations by mixed acid. Slow liquid-liquid reaction regime

Aromatic nitrations by mixed acid have been selected as a specific case of a heterogeneous liquid-liquid reaction. An extensive experimental programme has been followed using adiabatic and heat-flow calorimetry and pilot reactor experiments, supported by chemical analysis. A series of nitration experiments has been carried out to study the influences of different initial and operating conditions such as temperature, stirring speed and sulphuric acid concentration. In parallel, a mathematical model to predict the overall conversion rate has been developed. In this paper the mathematical modelling and the implementation and experimental validation for benzene, toluene and chlorobenzene mononitration in the kinetic control regime (slow liquid-liquid reaction) are presented and discussed.     

Closely Spaced Roots and Defectiveness in Second-Order Systems

When two closely spaced eigenvalues merge the associated eigenvectors can either (1) form a subspace where every vector in the span is an eigenvector or (2) coalesce into a single eigenvector. In the second alternative the repeated eigenvalue is associated with a bifurcation point in the eigenvector space and the system is said to be defective. In defective systems a set of coordinates that uncouple the dynamics does not exist and the closest thing possible is the basis of eigenvectors and generalized eigenvectors (sometimes called power vectors) that lead to the Jordan form. Although true defectiveness does not occur in practice, because eigenvalues are never exactly repeated, one anticipates that the features associated with defective conditions will have a bearing on the behavior of systems that are perturbed versions of defective ones. In viscously damped second order systems with symmetric matrices the potential for defectiveness is determined by the structure of the damping. This paper focuses on identification of conditions connecting the damping matrix with defectiveness. A numerical example of a two degree-of-freedom system that varies from being classically damped, to nonclassical, to defective, depending on the position of a dashpot, is used to illustrate the features of the eigensolution as defectiveness is approached.     

Surface functionalization without lattice degradation of highly crystalline nanoscaled carbon materials using a carbon monoxide atmospheric plasma treatment

Atmospheric plasma treatments on various forms of carbon were performed to compare the effect of surface modification using carbon monoxide (CO) as the active gas, in comparison to the conventionally used O₂. Changes in surface characteristics were analyzed using X-ray photoelectron spectroscopy (XPS) as a function of duration. The results indicated that use of O₂ plasma resulted in only a limited oxygen uptake (O/C = 0.11), while CO treatments resulted in tailorable surface O/C ratios as high as 0.69, a result not attainable when using low-pressure RF plasmas (O/C < 0.1). High-resolution XPS analysis and Auger spectroscopy confirmed that a tailorable level of carbonyl functional groups could be evenly distributed throughout the surface. Both Raman and scanning tunneling microscopy (STM) indicated nano-scale degradation of the structure when using the O₂ treatment. On the other hand, CO treated specimens exhibited no observable damage to the material with high levels of oxygen incorporation. Contact angle measurements verified the formation of a highly stable hydrophilic surface and excellent dispersion was observed in an aqueous solution on treated specimens after CO treatment. The CO treatment was also successfully applied to SWCNT with similar results and no degradation of structure.     

Strength improvements in toughened epoxy composites using surface treated GnPs

Nanographitic materials are gaining enormous interest as a new class of reinforcement for nanocomposites, promising revolutionary electrical, thermal, and mechanical properties. However, the progress has been quite limited especially in terms of mechanical properties. Here we report a significant leap, >2× increases in tensile strength and modulus of an epoxy composite using surface treated graphite nanoplatelets (GnPs). This corroborated by increases in Tgs as well as the presence of oxygen‐functionalized groups verified by XPS, suggest improved distribution and chemical interaction at the filler‐to‐matrix interface. Toughness values also showed increases with concentration, without compromising the strength or failure strain. However, if solvent levels during degassing were not reduced sufficiently, negligible contributions to strength and stiffness were observed with GnP loading. Subsequent elevated temperature treatments increased the strength of the composite due to cure enhancement of the matrix material, yet did not provide mechanical enhancements due to the incorporation of the filler. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40802.     

The effect of surface treatment on graphite nanoplatelets used in fiber reinforced composites

Atmospheric plasma treatment (APT) was used to surface‐activate graphite nanoplatelets (GnP) as well as highly graphitic P100 fibers used to manufacture composites. X‐ray photoelectron spectroscopy showed an increase in the O/C ratio of the treated surfaces when using either CO or O₂ as the active gas, whereas CO exhibited less damage to the treated reinforcement carbon material. APT of P100 fibers resulted in a 75% increase in composite tensile strength when compared to composites using untreated fibers. Surface treatment of GnPs also resulted in GnP/epoxy composites with significantly higher glass transition temperatures (Tg's) and 50% higher flexural strengths than those with no surface treatment because of stronger particle‐to‐resin coupling, which was also evidenced by the fracture surfaces. The effect of GnP loading concentration and plasma treatment duration was also evaluated on the tensile strength of fiber‐reinforced composites. The addition of untreated GnP filler resulted in a decrease in strength up to the 1% loading. However, higher loading conditions resulted in a 20% improvement because of GnP orientation effects. Fracture surfaces suggest that the fibers provided a mechanism for the GnPs to orient themselves parallel to the fiber axis, developing an oriented matrix microstructure that contributes to added crack deflection. Incorporating surface‐treated GnPs in these composites resulted in tensile strengths that were as high as 50% stronger than the untreated systems for all loading conditions. Increased GnP‐to‐matrix bonding as well as enhanced orientation of the GnPs resulted in multifunctional composites with improved mechanical performance. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39994.     

State Estimation in Structural Systems with Model Uncertainties

This paper presents an observer designed under the assumption that differences between predicted and measured outputs arise from discrepancies between the real structural system and the nominal model used to represent it. The observer gain is independent of the assumed model error parametrization and proves to be the transpose of the state to output matrix of a state space formulation. The estimated state with the proposed observer is shown to be identical to that obtained by exciting the nominal model with the known input while adjusting the measured portion of the state to match the measurements at the start of every step. Numerical experiments suggest that the proposed observer can provide state estimates that are substantially more accurate than results predicted by projecting the measurements in a truncated modal space.     

Model reference adaptive control with unknown relative degree

This work presents an indirect, model reference adaptive control for minimum phase linear systems of arbitrary relative degree. Global stability of the closed-loop system is proved in spite of bounded disturbances and asympotic tracking is achieved in the ideal case.     

Development of Wide-Spectrum Hybrid Bacteriocins for Food Biopreservation

The food industry demands new procedures and methods to produce minimally processed, ready to eat food with intact nutritional, taste, and flavor properties. The biopreservation and the use of both bacteriocins produced by lactic acid bacteria (LAB) and bacteriocinogenic strains as an alternative to substitute chemical antimicrobial for food preservation became increasingly important in the last two decades. When the new proposed natural preservatives techniques are applied, probiotics food can be obtained and, simultaneously, foodborne pathogens and spoilage contaminants can diminish. However, bacteriocins produced by LAB have a narrow antibacterial spectrum and are inactive against Gram-negative bacteria like Salmonella and the emergent enterohemorrhagic Escherichia coli. Knowing the mechanism of action and the structural features of microcins synthesized by Gram-negative bacteria and with potent antimicrobial activity against the mentioned microorganism, the proposal is to obtain hybrid peptides (microcin–bacteriocin) with broad antimicrobial spectrum. This review explains how the inability of bacteriocins to cross the outer membrane of Gram-negative bacteria unable them to act on the bacteria. It will also be discussed how a hybrid bacteriocin can be obtained.