Influence of water on the nanoindentation creep response of nylon 6

A nanoindentation system fitted with a fluid cell has been used to probe the influence of water on the nanoindentation creep response of commercial Nylon‐6 samples. Measurements on samples taken while immersed in deionized water were compared with measurements under usual ambient (～ 50% relative humidity) conditions. Water absorption reduces hardness by around 50% and elastic modulus by around 65%. The dimensionless creep parameter, A/d(0), where A is a constant and d(0) is the initial penetration at the start of the creep‐hold period, is a measure of the proportion of time‐dependent deformation compared with the total deformation. This parameter decreases significantly in water. We have suggested previously that A/d(0) correlates with tan δ. The observed reduction in A/d(0) when wet is consistent with a decrease in the tan δ peak due to a shift in the glass transition temperature when wet. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Antibacterial Activity and Amphidinol Profiling of the Marine Dinoflagellate Amphidinium carterae (Subclade III)

Microalgae have received growing interest for their capacity to produce bioactive metabolites. This study aimed at characterising the antimicrobial potential of the marine dinoflagellate Amphidinium carterae strain LACW11, isolated from the west of Ireland. Amphidinolides have been identified as cytotoxic polyoxygenated polyketides produced by several Amphidinium species. Phylogenetic inference assigned our strain to Amphidinium carterae subclade III, along with isolates interspersed in different geographic regions. A two-stage extraction and fractionation process of the biomass was carried out. Extracts obtained after stage-1 were tested for bioactivity against bacterial ATCC strains of Staphylococcus aureus, Enterococcus faecalis, Escherichia coli and Pseudomonas aeruginosa. The stage-2 solid phase extraction provided 16 fractions, which were tested against S. aureus and E. faecalis. Fractions I, J and K yielded minimum inhibitory concentrations between 16 μg/mL and 256 μg/mL for both Gram-positive. A targeted metabolomic approach using UHPLC-HRMS/MS analysis applied on fractions G to J evidenced the presence of amphidinol type compounds AM-A, AM-B, AM-22 and a new derivative dehydroAM-A, with characteristic masses of m/z 1361, 1463, 1667 and 1343, respectively. Combining the results of the biological assays with the targeted metabolomic approach, we could conclude that AM-A and the new derivative dehydroAM-A are responsible for the detected antimicrobial bioactivity.     

Equilibria in the alcoholysis reactions of terephthalic esters and chemical valorization of polyethyleneterephthalate waste. I. Equilibrium constants determination

The depolymerization of polyethyleneterephthalate (PET) by alcoholysis is an easy operation and gives interesting prospects for the valorization of wastes. The reactive species being composed of esters and alcohols, all possible alcoholysis reactions happen, whether wanted or not. Finally, a complex blend of many molecules follows. Practically, two great types of reactions occur: a reaction called “interchange,” and a reaction called “polycondensation.” We have determined the values of global equilibrium constants of those two types of reaction. The values of polycondensation equilibrium constants are close to those estimated from the “equireactivity” principle. We did not observe any particular behavior of monomer species. When reactants are the di‐ or mono‐propylene glycols, the molar proportion of these glycolic radicals is higher in the free glycols than in the polyester chains. Both proportions are similar, when diethylene glycol or 2‐ethylhexanol are used. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 329–340, 1999     

A Bayesian generalized Eyring-Weibull accelerated life testing model

In this paper, a novel approach to a Bayesian accelerated life testing model is presented. The Weibull distribution is used as the life distribution and the generalized Eyring model as the time transformation function. This is a model that allows for the use of more than one stressor, whereas other commonly used acceleration models, such as the Arrhenius and power law models, incorporate one stressor. The use of the generalized Eyring-Weibull model developed in this paper is demonstrated in a case study, where Markov chain Monte Carlo methods are utilized to generate samples for posterior inference.     

Authentication of Coffee Bean Variety by Near-infrared Reflectance Spectroscopy of Dried Extract

The potential of near-infrared (NIR) reflectance spectroscopy for discriminating between coffee beverage prepared from pure Arabica, pure Robusta and blends of these two varieties was investigated. Dried beverages were produced by both lyophilisation and air-drying under vacuum on glass-fibre filter paper. Spectral collections were treated by principal component and factorial discriminant analyses. Using the wavelength range 1100–2498 nm, only three of 65 test samples were misclassified when the filter paper approach was used. When freeze-dried coffee beverages were analysed, nine of the 65 test samples were misclassified. The basis for this discrimination appears to involve caffeine and/or other alkaloids.     

Uncertainty analysis in environmental modelling under a change of spatial scale

Although environmental processes at large scales are to a great degree the resultant of processes at smaller scales, models representing these processes can vary considerably from scale to scale. There are three main reasons for this. Firstly, different processes dominate at different scales, and so different processes are ignored in the simplification step of the model development. Secondly, input data are often absent or of a much lower quality at larger scales, which results in a tendency to use simpler, empirical models at the larger scale. Third, the support of the inputs and outputs of a model changes with change of scale, and this affects the relationships between them. Given these reasons for using different models at different scales, application of a model developed at a specific scale to a larger scale should be treated with care. Instead, models should be modified to suit the larger scale, and for this purpose uncertainty analyses can be extremely helpful. If upscaling disturbed the balance between the contributions of input and model error to the output error, then an uncertainty analysis will show this. Uncertainty analysis will also show how to restore the balance. In practice, application of uncertainty analysis is severely hampered by difficulties in the assessment of input and model error. Knowledge of the short distance spatial variability is of paramount importance to input error assessment with a change of support, but current geographical databases rarely convey this type of information. Model error can only be estimated reliably by validation, but this is not easy because the support of model predictions and validation measurements is usually not the same.     

The effects of dietary supplementation with Yucca schidigera extract or fractions thereof on nitrogen metabolism and gastrointestinal fermentation processes in the rat

Yucca schidigera was fractionated with butan-1-ol, yielding a butanol-extractable (BE) fraction, containing all the in vitro antimicrobial activity, and the aqueous, non-butanol-extractable (NBE) fraction. Four groups of five female rats (12 weeks old) were allowed ad libitum access to diets supplemented with water (control) or 200 mg kg⁻¹ total Y schidigera (TOT) or its fraction equivalent of NBE or BE for 64 days. The effects of the fractions and their interactions in the TOT treatment were analysed according to the factorial experimental structure by two-way ANOVA. NBE reduced serum urea (-50%, P=0·019) and ammonia (-46%, P=0·037) concentrations, serum/urine concentration quotients of urea (-79%, P=0·009) and ammonia (-57%, P=0·002). NBE also reduced hindgut acetate/propionate (-12%, P=0·007) but increased faecal ammonia concentration (+87%, P=0·039). BE reduced hindgut indoles (-25%, P=0·023) and interacted synergystically with NBE in the TOT treatment to further reduce hindgut acetate/propionate by 6% (P=0·006). NBE increased (+27%, P=0·002) and BE decreased (-57%, P=0·005) hindgut urease activity levels, resulting in essentially no change (+4%) in the TOT treatment. The in vitro antimicrobial activity of Y schidigera is an unlikely explanation for most of its effects in vivo because these are caused by NBE and in vitro antimicrobial activity is exclusive to BE. Sarsasapogenin and smilagenin were also exclusive (>98%) to BE and cannot account for the effects of Y schidigera on N metabolism. © 1998 SCI.     

Photoelectric Multilevel Memory Device based on Covalent Organic Polymer Film with Keto–Enol Tautomerism for Harsh Environments Applications

Covalent organic polymers (COPs) memristors with multilevel memory behavior in harsh environments and photoelectric regulation are crucial for high-density storage and high-efficiency neuromorphic computing. Here, a donor–acceptor (D–A)-type COP film (Py-COP-3), which is initiated by keto–enol tautomerism, is proposed for high-performance memristors. Satisfactorily, the indium tin oxide (ITO)/Py-COP-3/Ag device demonstrates multilevel memory performance, even in high temperatures, acid-base corrosion, and various organic solvents. Moreover, the performance can be modulated by the photoelectric effect to maintain a great switching behavior. By contrast, Py-COP-0, with similar structure and chemical composition to Py-COP-3 but without keto–enol tautomerism, exhibits binary storage performance. Further studies unravel that both the formation of conductive filaments and charge transfer within D-A Py-COP-3 film contribute to the resistive switching behavior of memory devices.     

Dynamic mechanical properties of UV-curable polyurethane acrylate with various reactive diluents

UV-curable polyurethane acrylate (PUA) based on polycaprolactone and m-tetramethylxylene diisocyanate were considered with different acrylate monomers as reactive diluents: ethylhexylacrylate, hexanediol diacrylate, and isobornyl acrylate. The effect of the chemical structure and functionality of the reactive diluent (33 wt %) on their thermal and mechanical properties were investigated. The synthetized PUA networks are homogeneous from a thermodynamical point of view. The initial glass transition temperature (T_g) and the functionality of the reactive diluent do not affect the onset value of the glass transition temperature of the network. Nevertheless, the main mechanical relaxation, denoted α, associated with the glass transition temperature becomes broader as the T_g of the homopolymer of the considered reactive diluent becomes higher than the T_g of the PU soft segments. The increase of the amount of the diacrylate monomer leads to an increase in the equilibrium and storage moduli in the rubbery state and to a decrease in the amplitude of the α relaxation. © 1996 John Wiley & Sons, Inc.