On the added value of multi-scale modeling of concrete

This review of the added value of multi-scale modeling of concrete is based on three representative examples. The first one is concerned with the analysis of experimental data, taken from four high-dynamic tests. The structural nature of the high-dynamic strength increase can be explained by using a multi-scale model. It accounts for the microstructure of the specimens. The second example refers to multi-scale thermoelastic analysis of concrete pavements, subjected to solar heating. A sensitivity analysis with respect to the internal relative humidity (RH) of concrete has underlined the great importance of the RH for an assessment of the risk of microcracking of concrete. The third example deals with multi-scale structural analysis of a real-scale test of a segmental tunnel ring. It has turned out that multi-scale modeling of concrete enables more reliable predictions of crack opening displacements in tunnel segments than macroscopic models taken from codes of practice. Overall, it is concluded that multi-scale models have indeed a significant added value. However, its degree varies with these examples. In any case, it can be assessed by means of a comparison of the results from three sources, namely, multi-scale structural analysis, conventional structural analysis, and experiments.     

Phthalhydrazide chemiluminescence method for determination of hydroxyl radical production: modifications and adaptations for use in natural systems

The hydroxyl radical is formed through a variety of processes pertinent to natural and anthropogenic systems. Here we report development of a simple and sensitive trap-and-trigger chemiluminescence method based upon the hydroxylation of phthalhydrazide to 5-hydroxy-2,3-dihydro-1,4-phthalazinedione, which emits chemiluminescence when oxidized under alkaline conditions. Cu(III) is employed as an oxidant and is shown to be relatively insensitive to a range of interferences likely to be encountered. The method has been standardized by use of γ-radiolysis of water as a primary source of hydroxyl radical, with a convenient secondary calibration procedure developed that uses Fenton chemistry. Detection limits varied from 7.4 nM (at pH 3) and 6.2 nM (at pH 8.1) of accumulated hydroxyl radical production in a simple 10 mM NaCl matrix to around 30 nM in an artificial seawater medium, due to competition for hydroxyl between the phthalhydrazide probe and bromide. The method has been used to characterize the kinetics of the Fenton system employed for calibration and is shown to be consistent with published models of this process over time scales of several hours. The application of this method to a range of matrices and for photochemical studies is also described.     

Optimization and evaluation of a sheathless capillary electrophoresis-electrospray ionization mass spectrometry platform for peptide analysis: comparison to liquid chromatography-electrospray ionization mass spectrometry

In this study we have evaluated the suitability of a sheathless capillary electrophoresis-electrospray ionization mass spectrometry (CE-ESI-MS) interface with a porous tip as the nanospray emitter for use in peptide analysis. A positively charged capillary coating and 0.1% formic acid as background electrolyte were used for separation upstream from mass spectrometry characterization. The influence of the distance between emitter tip and MS inlet, ESI voltage applied, and of the electroosmotic flow (EOF) on electrospray performance and efficiency of the system was investigated in detail. Under optimized conditions, less than 30 amol of a model peptide (angiotensin I) was required for a detection in the base peak electropherogram and positive identification via tandem MS. Three different cationic capillary coatings were investigated for stability, resolution, and EOF and were found to enable reproducible separations by CE-ESI-MS. After optimizing MS settings, the effectiveness of the CE-ESI-MS method developed was compared with a state-of-the-art nano-liquid chromatography (LC)-ESI-MS method by analyzing Arg-C-digested rat testis linker histones with both systems. With comparable amounts of sample applied, the number of identified peptides increased by more than 60% when using CE-ESI-MS. We found that low molecular mass peptides (below 1400 Da) were preferentially identified by CE-ESI-MS, since this group of peptides poorly interacted with the reversed-phase material in the nano-LC system. Finally, total analysis time in LC-ESI-MS for three runs including equilibration was nearly 4 times longer than that of CE-ESI-MS: 246 versus 66 min.     

Detection of synthetic testosterone use by novel comprehensive two-dimensional gas chromatography combustion-isotope ratio mass spectrometry

We report the first demonstration of comprehensive two-dimensional gas chromatography combustion-isotope ratio mass spectrometry (GC×GCC-IRMS) for the analysis of urinary steroids to detect illicit synthetic testosterone use, of interest in sport doping. GC coupled to IRMS (GCC-IRMS) is currently used to measure the carbon isotope ratios (CIRs, δ(13)C) of urinary steroids in antidoping efforts; however, extensive cleanup of urine extracts is required prior to analysis to enable baseline separation of target steroids. With its greater separation capabilities, GC×GC has the potential to reduce sample preparation requirements and enable CIR analysis of minimally processed urine extracts. Challenges addressed include online reactors with minimized dimensions to retain narrow peak shapes, baseline separation of peaks in some cases, and reconstruction of isotopic information from sliced steroid chromatographic peaks. Difficulties remaining include long-term robustness of online reactors and urine matrix effects that preclude baseline separation and isotopic analysis of low-concentration and trace components. In this work, steroids were extracted, acetylated, and analyzed using a refined, home-built GC×GCC-IRMS system. 11-Hydroxyandrosterone and 11-ketoetiocolanolone were chosen as endogenous reference compounds because of their satisfactory signal intensity, and their CIR was compared to target compounds androsterone and etiocholanolone. Separately, a GC×GC-quadrupole MS system was used to measure testosterone (T)/epitestosterone (EpiT) concentration ratios. Urinary extracts of urine pooled from professional athletes and urine from one individual that received testosterone gel (T-gel) and one individual that received testosterone injections (T-shots) were analyzed. The average precisions of δ(13)C and Δδ(13)C measurements were SD(δ(13)C) approximately ±1‰ (n = 11). The T-shot sample resulted in a positive for T use with a T/EpiT ratio of >9 and CIR measurements of Δδ(13)C > 5‰, both fulfilling World Anti-Doping Agency criteria. These data show for the first time that synthetic steroid use is detectable by GC×GCC-IRMS without the need for extensive urine cleanup.     

Synthesis and in vitro characterization of a novel PAA-ATP conjugate

The objective of this study was to improve the multifunctional properties of poly(acrylic acid) (PAA) by covalent attachment of 4-aminothiophenol (ATP) to its backbone. The permeation enhancing effect of PAA-ATP together with glutathione was evaluated in Ussing-type chambers using fluorescein isothiocyanate dextran as model compound. The mucoadhesive properties were evaluated in vitro on freshly excised porcine intestinal mucosa through the rotating cylinder method. The resulting conjugates PAA-ATP1 and PAA-ATP2 displayed 168 ± 35 and 426 ± 55 μmol immobilized free thiol groups per gram polymer, respectively. In addition, 279 ± 28 and 139 ± 22 μmol disulfide bonds per gram polymer, respectively, were identified on PAA-ATP1 and PAA-ATP2. Within disintegration studies in aqueous buffer solution, the modified polymers showed improved cohesive properties. Because of the immobilization of ATP, the swelling of PAA-ATP1 and PAA-ATP2 improved 12.0- and 17.8-fold, respectively. The adhesion times of the conjugates PAA-ATP1 and PAA-ATP2 were more than 20- and 30-fold increased in comparison to unmodified PAA. Furthermore, conjugates PAA-ATP1 and PAA-ATP2 exhibited a 1.86- and 2.07-fold higher permeation enhancing effect, respectively, over unmodified PAA. According to these results, PAA-ATP conjugates represent a very promising novel type of thiomer for the development of various mucoadhesive drug delivery systems.     

Novel chaotic behavior in the Muthuswamy–Chua system using Chebyshev Polynomials

In this paper, three kinds of memristors with memristance functions obtained from the Chebyshev polynomials are used in the Muthuswamy–Chua system, which has only three circuit elements: a linear passive inductor, a linear passive capacitor and a nonlinear active memristor. We use multivariable second‐order polynomial functions of current and memristor state for the internal state function of the memristor. This enables our system to generate not only double‐scroll but also four‐scroll attractors. Systematic studies of chaotic behavior in these systems are performed using phase portraits, bifurcation diagrams and Lyapunov exponents. Simulation results show that all these systems exhibit chaotic behavior over a range of control parameters. Copyright © 2014 John Wiley & Sons, Ltd.     

Biodegradation of plant cell walls,wall carbohydrates,and wall aromatics in wheat grown in ambient or enriched CO2 concentrations

Mature internodes from wheat (Triticum aestivum L) grown in control (ambient at c 370 μnol mol^?1) or enriched (to 550 μmol mol^?1) concentrations of atmospheric CO₂ in the free-air CO₂ enrichment (FACE) system were analyzed for potential changes in biodegradation of constituents due to predicted increases in atmospheric levels of CO₂. The first internodes below the grain were incubated with the lignocellulose-degrading white rot fungus, Phanerochaete chrysosporium K-3, or incubated without microorganisms. Plant samples were then analyzed for dry weight loss, disposition of specific cell types to biodegradation using electron microscopy, carbohydrates and lignin using solid state NMR spectroscopy, and ester-and ether-linked aromatics using gas chromatography. Phanerochaete chrysosporium extensively degraded stems cells (c 75%) and both carbohydrate and aromatic portions of the wheat stems; proportionately more carbohydrates were removed by the fungus from the stems. Enriched CO₂ did not affect the chemical composition of wheat stems or the biodegradation by P chrysosporium of plant cell walls or wall components for the most part. Data from various methods all indicated that enriched CO₂ did not substantially alter the biodegradation of wheat cell wall internodes or wall components. Evidence was not found for an influence on C cycling due to CO₂ concentrations in this study.