Parametric sensitivity and runaway in chemical reactors

In certain regions of operating conditions, chemical reactors may exhibit parametric sensitivity; i.e., small changes in one or more of the reactor input parameters lead to much larger changes in the output variables. Since such behaviour leads to deleterious performance, it is of practical interest to identify regions of parametric sensitivity in the reactor parameter space. Until recently, this could be done only to describe thermal runaway, and only for those systems where a temperature profile could be defined. Both of these limitations can be removed by consideringthe generalized criterion for parametric sensitivity, whereby sensitivity ofany output of the model toany input can be treated. Applications of the generalized criterion are discussed, with specific examples including pseudohomogeneous and heterogeneous model tubular reactors, a nonisothermal CSTR, and a polymerization reactor. Dedicated to Dr L K Doraiswamy — Gentleman, Scholar, Friend — on his sixtieth birthday.     

Liquid-crystallization induced reactions. Microstructure and morphology of copolyesters synthesized by transesterification of PET with some LCP monomers

The transesterification of poly(ethylene terephthalate) (PET) with a mixture of sebacic acid (S), 4,4′-diacetoxybiphenyl (B) and 4-acetoxybenzoic acid (H), carried out under conditions expectedly favoring the formation of a p(ET-SBH) random copolyester, produces biphasic materials with an isotropic matrix and a highly fibrous, liquid-crystalline dispersed phase. Spectroscopic, calorimetric, microscopic and diffractometric characterization of the fractions separated by solvent extraction has shown that the two phases consist of practically random copolyesters having different average composition. Interestingly, the degree of aromaticity of the matrix is even lower than that of PET, whereas that of the minor phase is appreciably higher than that calculated for the SBH copolyester that would be produced from the monomer mixture in the absence of PET. This unexpected result is interpreted on the basis of an enthalpy-driven progressive diffusion of aromatic-rich material toward the mesophase which segregates at an early stage of the polycondensation within the isotropic mixture of low molar mass oligomers initially produced by the PET acidolysis. Thus, an increasing differentiation, rather than an equilibration, of the composition of the two phases takes place. It is noteworthy that, despite the strong compositional difference, the two phases of these products show fairly good compatibility and interfacial adhesion.     

A comparison of bibliometric indicators for computer science scholars and journals on Web of Science and Google Scholar

Given the current availability of different bibliometric indicators and of production and citation data sources, the following two questions immediately arise: do the indicators’ scores differ when computed on different data sources? More importantly, do the indicator-based rankings significantly change when computed on different data sources? We provide a case study for computer science scholars and journals evaluated on Web of Science and Google Scholar databases. The study concludes that Google scholar computes significantly higher indicators’ scores than Web of Science. Nevertheless, citation-based rankings of both scholars and journals do not significantly change when compiled on the two data sources, while rankings based on the h index show a moderate degree of variation.     

Pathogenic Mutations Shift the Equilibria of α‐Synuclein Single Molecules towards Structured Conformers

α‐synuclein (α‐Syn) is an abundant brain protein whose mutations have been linked to early‐onset Parkinson's disease (PD). We recently demonstrated, by means of a single‐molecule force spectroscopy (SMFS) methodology, that the conformational equilibrium of monomeric wild‐type (WT) α‐Syn shifts toward β‐containing structures in several unrelated conditions linked to PD pathogenicity. Herein, we follow the same methodology previously employed for WT α‐Syn to characterize the conformational heterogeneity of pathological α‐Syn mutants A30P, A53T, and E46K. Contrary to the bulk ensemble‐averaged spectroscopies so far employed to this end by different authors, our single‐molecule methodology monitored marked differences in the conformational behaviors of the mutants with respect to the WT sequence. We found that all the mutants have a much higher propensity than the WT to adopt a monomeric compact conformation that is compatible with the acquiring of β structure. Mutants A30P and A53T show a similar conformational equilibrium that is significantly different from that of E46K. Another class of conformations, stabilized by mechanically weak interactions (MWI), shows a higher variety in the mutants than in the WT protein. In the A30P mutant these interactions are relatively stronger, and therefore the corresponding conformations are possibly more structured. The more structured and globular conformations of the mutants can explain their higher propensity to aggregate with respect to the WT.     

A rapid spectroscopic method to detect the fraudulent treatment of tuna fish with carbon monoxide

Carbon monoxide (CO) can be used to treat fresh meat and fish in order to retain its ‘fresh’ red colour appearance for a longer period of time. In fact, upon aging, myoglobin is oxidized to met-myoglobin with the concomitant blue-shift and broadening of the Soret maximum, which brings about a change in the colour of the fish, revealing that it is no longer fresh. The use of carbon monoxide, which reacts with the oxy-myoglobin to form a fairly stable cherry red carboxy-myoglobin complex may mask spoilage, because the CO-complex can be stable beyond the microbiological shelf life of the meat. The presence of CO in tuna fish has been investigated by optical spectroscopy as the formation of the CO adduct can be easily detected by the combined analysis of electronic absorption spectra in their normal and second derivative modes, monitoring the intense Soret band at 420 nm. The presence of met- and oxy-myoglobin can obscure the presence of small amounts of the CO adduct; however, it can be revealed by chemically reducing the met- and oxy-forms to the deoxy-form in an anaerobic environment. This spectroscopic method provides a qualitatively rapid laboratory screening procedure for food control to unmask the presence of CO in frozen or fresh fish.     

Development of an HS-SPME-GC method to determine the methyl anthranilate in Citrus honeys

An efficient and simple method for determination of methyl anthranilate (MA) in Citrus spp. honeys by headspace-solid-phase microextraction-gas chromatography (HS-SPME-GC) was developed and validated. Experimental design was used to investigate the effects of the principal extraction parameters. The central composite design (CCD) and the desirability function were used to find the experimental conditions providing the optimal HS-SPME result. Validation was carried out in terms of specificity, linearity, limit of detection (LOD) and quantitation (LOQ) (0.149 and 0.324 μg/g, respectively), method precision (RSD 7%), LOQ precision (RSD 6.5%), and was resulted accurate and robust. Finally, the applicability of the method to the determination of MA in a number of commercial Citrus spp. honey samples was demonstrated, the content ranged from 0.63 to 3.26 μg/g.     

Study of some factors involved in ethanal production during alcoholic fermentation

The influence of temperature, turbidity and oxygen uptakes to the musts on the production of ethanal by yeasts, during the alcoholic fermentation (AF), has been studied. The aim was to evaluate how increasing and controlling the production of this molecule, in order to anticipate the reactions between anthocyanins and flavans from the second half of the AF. This concerns, in particular, those winemaking techniques consisting in a temporarily separate fermentation of a part of the must (35–40% of the total mass), that is drained before the start of the AF. The experimental design was a complete factorial plan with three factors upon two levels (T = 18 °C and 22 °C; with or without oxygen; turbidity of 30 and 120 NTU); data were elaborated with 3-ways ANOVA. Temperature proved to be the main factor influencing ethanal production during AF: higher temperatures (22 °C versus 18 °C) cause an increase of the ethanal content during the first days of fermentation; after having reached 6–7% of ethanal, the effect is inverted. The influence of turbidity is less important, and it's synergic with the effect of temperature. Oxygen has a detrimental effect on the production of ethanal only at the beginning of the AF, while later, in presence of ethanol, it promotes it through a chemical way.