Blends containing amphiphilic polymers IV. Poly(N‐1‐alkyl itaconamic acids) with poly(2‐vinylpyridine) and poly(4‐vinylphenol)

The phase behavior of blends containing Poly(N‐1‐alkyl itaconamic acids) (PNAIA) with Poly(2‐vinylpyrindine) (P2VPy) and Poly(4‐vinylphenol) (P4VPh) were analyzed by Diferential Scanning Calorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FTIR). Miscibility over the whole range of compositions is observed in both systems. All the blends show thermograms exhibiting distinct single glass transition temperatures (T_g), which are intermediate to those of the pure components. The Calorimetric Analysis using Gordon Taylor, Couchman, and Kwei treatments allows conclusion that interactions between the components is favorable to the miscibility. FTIR analysis of the blends suggests that the driving force for miscibility is hydrogen bonding formation. The variation of the absorptions of the carbonyl groups of PNAIA and the hydroxyl groups of P4VPh allows one to attribute the miscibility to weak acid base like interactions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1245–1250, 2002; DOI 10.1002/app.10453     

Stabilization of Telomeric I‐Motif Structures by (2′S)‐2′‐Deoxy‐2′‐C‐Methylcytidine Residues

G‐quadruplexes and i‐motifs are tetraplex structures present in telomeres and the promoter regions of oncogenes. The possibility of producing nanodevices with pH‐sensitive functions has triggered interest in modified oligonucleotides with improved structural properties. We synthesized C‐rich oligonucleotides carrying conformationally restricted (2′S)‐2′‐deoxy‐2′‐C‐methyl‐cytidine units. The effect of this modified nucleoside on the stability of intramolecular i‐motifs from the vertebrate telomere was investigated by UV, CD, and NMR spectroscopy. The replacement of selected positions of the C‐core with C‐modified residues induced the formation of stable intercalated tetraplexes at near‐neutral pH. This study demonstrates the possibility of enhancing the stability of the i‐motif by chemical modification.     

Modeling considerations in seismic assessment of RC bridges using state-of-practice structural analysis software tools

The increasing awareness of the general society toward the seismic safety of structures has led to more restrictive performance requirements hence, many times, to the need of using new and more accurate methods of analysis of structures. Among these, nonlinear static procedures are becoming, evermore, the preferred choice of the majority of design codes, as an alternative to complete nonlinear time-history analysis for seismic design and assessment of structures. The many available software tools should therefore be evaluated and well understood, in order to be easily and soundly employed by the practitioners. The study presented herein intends to contribute to this need by providing further insight with respect to the use of commonly employed structural analysis software tools in nonlinear analysis of bridge structures. A comparison between different nonlinear modeling assumptions is presented, together with the comparison with real experimental results. Furthermore, alternative adaptive pushover procedures are proposed and applied to a case study bridge, based on a generic plastic hinge model. The adopted structural analysis program proved to be accurate, yielding reliable estimates, both in terms of local plastic hinge behavior and global structural behavior.     

Wetting Behavior of Ibuprofen Racemate Surfaces

The wetting behavior and detailed surface energetics of a racemate crystalline system were measured via contact angle measurements and inverse gas chromatography at finite concentrations. The advancing contact angles for water, diiodomethane, formamide, and ethylene glycol were measured on specific facets for racemic ibuprofen and S-(+)-ibuprofen single macroscopic crystals, and were found to be facet dependent for both systems. This observation demonstrates that variation in molecular orientation within the crystal lattice results in variations in exposed surface chemistry for differing facets, which results in anisotropic wetting behavior as previously reported. Surface free energy profiles of the ibuprofen racemates determined using a novel inverse gas chromatography method showed that powder samples (75–150 µm particle diameter) exhibited relatively homogeneous surface energies, with similar values of γ_SV ^d to those obtained by the contact angle analysis. These results lead us to conclude that ibuprofen exhibited a low level of surface heterogeneity, with the dominant facet of these powders exhibiting a low γ_SV ^d, with high energetic sites estimated to be < 3% of exposed available surface.     

Influence of operational parameters on the performance of PEMFCs with serpentine flow field channels having different (rectangular and trapezoidal) cross-section shape

The effect of operational parameters on the performance of PEMFCs by using serpentine flow field channels with different (rectangular and trapezoidal) cross-section shape has been investigated. More than cell temperature and pressure, reactant humidification temperature (T_ha,c) has a significant influence on the effect of serpentine channels with trapezoidal cross-section on cell performance. The high capability of water removal by serpentine channels with trapezoidal cross-section positively affects the fuel cell performance when the water content in the system is high, as in the case of the reactant humidification temperature higher than cell temperature (T_c). On the contrary, when the water content in the cell is low, as in the case of T_ha,c = T_c, the high ability of water removal of serpentine channels with trapezoidal cross-section results in a less effective membrane/cathode hydration. Conversely, the effect of T_ha,c on the performance of the cell with serpentine channels with rectangular cross-section is negligible.     

Comparative study between ANN models and conventional equations in the analysis of fatigue failure of GFRP

The purpose of this paper is to assess the applicability of two artificial neural networks (ANN) architecture, perceptron ANN, modular ANN, and Adam’s equation in the modeling of fatigue failure in polymer composites, more specifically in glass fiber reinforced plastic (GFRP). In the application of the model using ANN we show the feasibility of obtaining good results with a small number of S–N curves. The other model used involves applying empirical equations known as Adam’s equations. A comparative study on the application of the aforementioned models is developed based on statistical tools such as correlation coefficient and mean square error. For this analysis we used composite materials in the form of laminar structures with distinct stacking sequences, which are applied industrially in the construction of large reservoirs. Reinforcements consist of mats and bidirectional textile fabric made of E-glass fibers soaked in unsaturated orthophthalic polyester resin. These were tested for six different stress ratios: R = 1.43, 10, ?1.57, ?1, 0.1, and 0.7. The results showed that although ANN modeling is in the initial phase, it has great application potential.     

The effect of cocoa fermentation and weak organic acids on growth and ochratoxin A production by Aspergillus species

The acidic characteristics of cocoa beans have influence on flavor development in chocolate. Cocoa cotyledons are not naturally acidic, the acidity comes from organic acids produced by the fermentative microorganisms which grow during the processing of cocoa. Different concentrations of these metabolites can be produced according to the fermentation practices adopted in the farms, which could affect the growth and ochratoxin A production by fungi. This work presents two independent experiments carried out to investigate the effect of some fermentation practices on ochratoxin A production by Aspergillus carbonarius in cocoa, and the effect of weak organic acids such as acetic, lactic and citric at different pH values on growth and ochratoxin A production by A. carbonarius and Aspergillus niger in culture media. A statistical difference (ρ<0.05) in the ochratoxin A level in the cured cocoa beans was observed in some fermentation practices adopted. The laboratorial studies demonstrate the influence of organic acids on fungal growth and ochratoxin A production, with differences according to the media pH and the organic acid present. Acetic acid was the most inhibitory acid against A. carbonarius and A. niger. From the point of view of food safety, considering the amount of ochratoxin A produced, fermentation practices should be conducted towards the enhancement of acetic acid, although lactic and citric acids also have an important role in lowering the pH to improve the toxicity of acetic acid.     

Electrical properties of Ca-doped ceria electrolytes prepared by proteic sol-gel route and by solid-state reaction using mollusk shells

Ca-doped ceria (CCO) electrolytes were prepared using two processing approaches, proteic sol-gel synthesis using gelatin (SG) and solid-state reaction (SSR). Mollusk shell powder was used in the SSR method as the main source of Ca. Materials sintered at 1350–1450 °C exhibited relative density above 95% and different microstructural features regarding grain size and morphology. Impedance spectroscopy in air revealed a comparatively better total electrical response of materials prepared by the proteic sol-gel route. CCO ceramics prepared by the SG route have bulk conductivity four times higher than the highest conductivity of samples processed by the SSR route. Electrical properties of the grain boundaries of both series of materials reveal distinct oxygen vacancy concentration profiles and space charge potentials. The role of processing route and sintering schedules was discussed taking into consideration the distinct impact of Ca interaction in the grain boundaries.     

Voltammetric behaviour of mitoxantrone at a DNA-biosensor

The surface of an electrochemical glassy carbon electrode was modified with a layer of double-stranded DNA (dsDNA) or with double-stranded DNA conditioned in single-stranded DNA (ssDNA) and was used to investigate mitoxantrone-DNA interactions. Differential pulse and square wave voltammetry were applied to develop an electroanalytical procedure for the determination of mitoxantrone and evaluate its interaction with dsDNA or ssDNA immobilized on the electrode surface. The results demonstrate that MTX interaction with DNA is not specific to either guanine or adenine bases. The kinetics of the mitoxantrone-DNA interaction is slow and damage to DNA was followed with time.